DESCRIPTION VENTILATOR Field of the Invention [0001] The present invention relates to a ventilator used for exchanging air between the inside and the outside of a building. Background of the Invention [0002] A ventilator of this kind generally includes a body and an opening-closing member as disclosed in the Patent Document 1 listed below. The body may be fixed to a wall or a window of a building and a ventilation passage for communication between the inside and outside of the building is disposed inside the body. The opening-closing member is provided for opening and closing the ventilation passage and is movably disposed inside the body. [0003] One side portion of the opening-closing member along a moving direction thereof is supported by the body such that the opening-closing member is rotatable and linearly movable. The opening-closing member is linearly movable between a first position and a second position and is rotatable between a closing position and an opening position. [0004] A first cam mechanism and a second cam mechanism are provided between the body and the other side portion of the opening-closing member. The first cam mechanism causes the opening-closing member to be rotated in a direction from the opening position to the closing position when the body is linearly moved in a direction (to be referred to as "first direction" hereinafter) from the second position to the first position. When the opening-closing member reaches the first position, the first cam mechanism causes the opening-closing member to be rotated to the closing position. When the opening-closing member is rotated to the closing position, the opening-closing member is abutted against the body via a sealing member and closes the ventilation passage. Thereby, the exchange of air between the inside and the outside is stopped. [0005] The second cam mechanism causes the opening-closing member to be rotated from the closing position toward the opening position when the body is linearly moved in a direction (to be referred to as "second direction" hereinafter) from the first position to the second position. When the opening-closing member reaches the second position, the second cam mechanism causes the opening-closing member to be rotated to the opening position. When the opening-closing member is rotated to the opening position, the opening-closing member opens the ventilation passage. Thereby, the air is exchanged between the inside and the outside. [0006] The first cam mechanism includes an inclined surface inclined with respect to a direction of linear movement of the opening-closing member and a pressing surface that is parallel to the direction of linear movement of the opening-closing member. The inclined surface is contacted with the opening-closing member when the opening-closing member is linearly moved in the first direction and causes the opening-closing member to be rotated from the opening position to the closing position. When the opening-closing member is moved further in the first direction and reaches the first position, the opening-closing member is moved beyond the inclined surface and pressingly contacted with the pressing surface. In this condition, the opening-closing member is not rotated and maintained at a stopped state since the pressing surface is parallel to the direction of linear movement of the opening-closing member. In other words, the opening-closing member is maintained at the closing position.
Prior Art Documents Patent Documents [0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-234673 Summary of the Invention Problem to be Solved by the Invention [0008] Manufacturing errors are inevitable with the body and the opening-closing member. The manufacturing errors may affect accuracy of position of the pressing surface and a contact surface of the body against which the opening-closing member is abutted when rotated to the closing position. As a result, the opening-closing member may press the body with an excessive force or, conversely, with an insufficient force when the opening-closing member is rotated to the closing position. If a pressure of the opening-closing member contacting the body is excessive, it may become difficult for the opening-closing member to be linearly moved or it may cause excessive compression of the sealing member, leading to an early deterioration of the sealing member. Conversely, if the pressure of the opening-closing member contacting the body is insufficient, airtightness of the opening-closing member sealing the ventilation passage may be reduced. Solution to the Problem [0009] The present invention provides a ventilator comprising: a body having a ventilation passage formed therein, an outside and an inside communicating with each other through the ventilation passage; an opening-closing member movably disposed in the body; a first cam mechanism disposed between the body and the openingclosing member, the first cam mechanism causing the opening-closing member to be moved from an opening position to a closing position when the opening-closing member is moved in a first direction, the opening-closing member opening the ventilation passage when at the opening position, the opening-closing member closing the ventilation passage when at the closing position; a second cam mechanism disposed between the body and the opening-closing member, the second cam mechanism causing the opening-closing member to be moved from the closing position to the opening position when the opening-closing member is moved in a second direction opposite to the first direction; and a first reference portion disposed in the body, the first reference portion determining the closing position of the opening-closing member by abutting against the opening-closing member, wherein a first biasing mechanism is disposed in the body; and the first biasing mechanism presses the opening-closing member at the closing position against the first reference portion by biasing the opening-closing member in a direction from the opening position to the closing position, thereby maintaining the opening-closing member at the closing position. Preferably, the first cam mechanism comprises a first cam part disposed in one of the body and the opening-closing member and a first abutment portion disposed in the other of the body and the opening-closing member; when the opening closing member is moved in the first direction, the first abutment portion slides on the first cam part, thereby causing the opening-closing member to be moved from the opening position to the closing position; the second cam mechanism comprises a second cam part disposed in the one of the body and the opening-closing member and a second abutment portion disposed in the other of the body and the opening-closing member; when the opening-closing member is moved in the other direction, the second abutment portion slides on the second cam part, thereby causing the opening closing member to be moved from the closing position to the opening position; an elastically deformable first elastic portion is disposed in a front end portion of the first cam part located at a front in the first direction; and the first elastic portion serves as the first biasing mechanism that presses the opening-closing member against the first reference portion by biasing the first abutment portion in the direction from the opening position to the closing position. Preferably, the first cam part comprises a first support portion and a first plate made of metal, the first support portion disposed in the one of the body and the opening-closing member; the first support portion comprises a first inclined surface inclined with respect to the first direction and the second direction; the first plate is disposed in the one of the body and the opening-closing member such that the first plate is contacted with the first inclined surface; when the opening-closing member is moved in the one direction, the first abutment portion is slidingly contacted with the first inclined surface via the first plate, thereby causing the opening-closing member to be moved in the direction from the opening position to the closing position; and a front end portion of the first plate located at a front in the first direction to be spaced from the first inclined surface in the direction from the opening position to the closing position, the front end portion of the first plate serving as the first elastic portion. Preferably, the second cam part comprises a second support portion and a second plate made of metal, the second support portion disposed in the one of the body and the opening-closing member; the second support portion comprises a second inclined surface inclined with respect to the first direction and the second direction; the second plate is disposed in the one of the body and the opening-closing member such that the second plate is contacted with the second inclined surface; when the opening-closing member is moved in the other direction, the second abutment portion is slidingly contacted with the second inclined surface via the second plate, thereby causing the opening-closing member to be moved in the direction from the closing position to the opening position. Preferably, the first cam part comprises a second reference portion disposed continuously from a rear end portion of the first inclined surface located at a rear in the first direction; the first plate comprises an extension portion disposed in a rear end portion thereof located at a rear in the first direction, the extension portion contacted with the second reference portion; the opening position of the opening-closing member is determined by abutment of the first abutment portion against the second reference portion via the extension portion; the second plate comprises an elastically deformable second elastic portion disposed in a front end portion thereof located at a front in the second direction; and the second elastic portion presses the second abutment portion against the second reference portion via the extension portion by biasing the second abutment portion in the direction from the closing position to the opening position, thereby maintaining the opening-closing member at the opening position. Preferably, cam blocks made of hard resin are fixed to the body; and the first cam mechanism and the second cam mechanism are disposed between the cam blocks and the opening-closing member. Preferably, the first cam mechanism comprises a first cam part disposed in the cam blocks and a first abutment portion disposed in the opening-closing member; when the opening-closing member is moved in the first direction, the first abutment portion slides on the first cam part, thereby causing the opening-closing member to be moved from the opening position to the closing position; the second cam mechanism comprises a second cam part disposed in the cam blocks and a second abutment portion disposed in the opening-closing member; when the opening-closing member is moved in the second direction, the second abutment portion slides on the second cam part, thereby causing the opening-closing member to be moved from the closing position to the opening position; an elastically deformable first elastic portion is disposed in a front end portion of the first cam part located at the front in the first direction; and the first elastic portion serves as the first biasing mechanism that presses the opening-closing member against the first reference portion by biasing the first abutment portion in the direction from the opening position to the closing position. Preferably, the first cam part comprises a first support portion disposed in the cam blocks and a first plate made of metal; the first support portion comprises a first inclined surface inclined with respect to the first direction and the second direction; the first plate is disposed in the cam blocks such that the first plate is contacted with the first inclined surface; when the opening-closing member is moved in the first direction, the first abutment portion is slidingly contacted with the first inclined surface via the first plate, thereby causing the opening-closing member to be moved in the direction from the opening position to the closing position; and a front end portion of the first plate located at a front in the first direction to be spaced from the first inclined surface in the direction from the opening position to the closing position, the front end portion serving as the first elastic portion. Preferably, the second cam part comprises a second support portion disposed in the cam blocks and a second plate made of metal; the second support portion comprises a second inclined surface inclined with respect to the first direction and the second direction; the second plate is disposed in the cam blocks such that the second plate is contacted with the second inclined surface; when the opening-closing member is moved in the second direction, the second abutment portion is slidingly contacted with the second inclined surface via the second plate, thereby causing the opening-closing member to be moved in the direction from the closing position to the opening position. Preferably, the first cam part comprises a second reference portion disposed continuously from a rear end portion of the first inclined surface located at a rear in the first direction; the first plate comprises an extension portion disposed in a rear end portion thereof located at a rear in the first direction, the extension portion contacted with the second reference portion; the opening position of the opening-closing member is determined by the abutment of the first abutment portion against the second reference portion via the extension portion; the second plate comprises an elastically deformable second elastic portion disposed in a front end portion thereof located at a front in the second direction; and the second elastic portion presses the second abutment portion against the second reference portion via the extension portion by biasing the second abutment portion in the direction from the closing position to the opening position, thereby maintaining the opening-closing member at the opening position. Preferably, the first plate and the second plate are formed in a same shape. Advantageous Effects of the Invention [0010] In the ventilator according to the present invention, even if there are manufacturing errors in the body or the opening-closing member, such manufacturing errors can be absorbed by the first biasing mechanism because the opening-closing member is pressed against the first reference portion by the first biasing mechanism. Therefore, the opening-closing member can be pressed against the first reference portion with the right amount of force. Brief Description of the Drawings [0011] FIG. 1 shows a portion of a building in which a ventilator according to the present invention is used viewed from an inside of the building. FIG. 2 is an enlarged cross-sectional view taken along line A-A of FIG. 1. FIG. 3 is an enlarged cross-sectional view taken along line B-B of FIG. 1. FIG. 4 is a plan view of an embodiment of the ventilator according to the present invention. FIG. 5 is a perspective view of the embodiment shown in a condition in which a lid is separated from a body. FIG. 6 is an exploded perspective view of the embodiment, showing the body, an opening-closing member and cam blocks. FIG. 7A is a cross-sectional view taken along line X-X of FIG. 4, shown in a condition in which the opening-closing member is in an closing position. FIG. 7B is a cross-sectional view taken along line X-X of FIG. 4, shown in a condition in which the opening-closing member is in an opening position.
FIG. 8 is a cross-sectional view taken along line X-X of FIG. 7A. FIG. 9 is a cross-sectional view taken along line Y-Y of FIG. 7B. FIG. 10 is a front view of a lever support member adopted in the embodiment. FIG. 11 is a front view of a lever adopted in the embodiment. FIG. 12 is a front view of a link bar adopted in the embodiment. FIG. 13 is a front view of a connecting member adopted in the embodiment. FIG. 14 is an enlarged view of a main portion of FIG. 7A. FIG. 15 is an enlarged view of a main portion of FIG. 7B. FIG. 16 is an enlarged front view of the cam block, a first plate and a second plate adopted in the embodiment. FIG. 17A is a front view of the cam block adopted in the embodiment. FIG. 17B is a rear view of the cam block adopted in the embodiment. FIG. 17C is a bottom view of the cam block adopted in the embodiment. FIG. 17D is a side view of the cam block adopted in the embodiment. FIG. 17E is a cross-sectional view taken along line X-X of FIG. 17A. FIG. 18A is a front view of the first plate adopted in the embodiment. FIG. 18B is a side view of the first plate adopted in the embodiment. Description of the Preferred Embodiments [0012] A preferred embodiment of the present invention will be described hereinafter with reference to FIGS. I to 18 attached hereto. FIG. 1 is a front view of a building in which a ventilator according to the present invention is used, with the building viewed from an inside I to an outside 0. In this building, a riser A that rises from a floor level FL by a predetermined height (about 30 to 50 cm, for example) is provided. An upper rail B is provided above the riser A. A multitude of stiles C spaced from each other in a left-right direction are provided between the riser A and the upper rail B. A window glass D is supported by the riser A, the upper rail B and two of the stiles C, C adjacent to each other in the left-right direction. [0013] As shown in FIG. 3, a ventilation duct E is provided in the riser A. One end portion of the ventilation duct E is open to an outer surface of the riser A facing the outside 0. The other end portion of the ventilation duct E is open to an upper surface of the riser A facing the inside I. A net F for preventing relatively large trashes and small animals from entering into the ventilation duct E is removably disposed at the end portion of the ventilation duct E facing the outside 0. As shown in FIGS. 2 and 3, the ventilator 1 according to the present invention is removably disposed at the end portion of the ventilation duct E facing the inside I such that the ventilator 1 can be mounted and dismounted from the inside I. [0014] Features of the ventilator 1 will be described below. Directions used in the description of the features of the ventilator 1 refer to an inside-outside direction, left right direction and a vertical direction of the building for the sake of convenience. It is to be understood that features of the ventilator 1 is not limited by these directions. [0015] As shown in FIGS. 5 and 6, the ventilator 1 includes a body 2. The body 2 includes a body member 2a and a pair of end members 2b, 2b. The body member 2a is made of an aluminum extruded material and is formed to have a U-shaped cross section. The end members 2b, 2b are made of an aluminum extruded material and are formed to have L-shaped cross-sections. The end members 2b, 2b are respectively fixed to opposite end portions of the body 2. Accordingly, opposite end openings of the body member 2a are closed by the end members 2b, 2b, and the body 2 as a whole is formed in a shape of a box that is open in an upper portion thereof. [0016] As shown in FIGS. 5, 8 and 9, a cover lid 3 is fixed to an upper end portion of the body 2. The cover lid 3 is longer than the body 2 in the left-right direction and wider than the body 2 in the inside-outside direction. The cover lid 3 is disposed so as to cover the entire opening in the upper portion of the body 2. Engagement portions 3a are respectively disposed in side surfaces of the cover lid 3 respectively facing the inside I and the outside 0. Lock members 4 are respectively disposed in side surfaces of the body 2 respectively facing the inside I and the outside 0. The cover lid 3 is removably attached to the body 2 with the cover lid 3 pressed against a top surface of the body 2 by disengageable engagement of the lock members 4 with the engagement portions 3a. The cover lid 3 is contacted with the upper surface of the body 2 via a seal member Si. Thereby, the body 2 and the cover lid 3 are sealed in an airtight manner. [0017] As shown in FIGS. 8 and 9, the body 2 is disposed at the end portion of the ventilation duct E facing the inside I. Catch portions Al are formed in a wall of the ventilation duct E. The body 2 is removably mounted inside the ventilation duct E in the riser A such that the body 2 can be mounted and dismounted from the inside I by disengageable engagement of the lock members 4 with the catch portions Al. In a condition where the body 2 is mounted in the riser A, a top surface of the cover lid 3 is arranged coplanarly with the top surface of the riser A. Alternatively, the body 2 may be removably mounted to the riser A by disposing screws (not shown) through holes 2c formed in the end members 2b and by screwing and securing the screws into the riser A. [0018] As shown in FIG. 3, a dividing wall portion A2 is formed in the riser A. The dividing wall portion A2 divides the ventilation duct E into a portion closer to the outside 0 and a portion closer to the inside I. A through hole A3 is formed in the dividing wall portion A2. The portion of the ventilation duct E closer to the outside 0 and the portion of the ventilation duct E closer to the inside I than the dividing wall portion A2 are communicated via the through hole A3. [0019] An undersurface of a bottom wall portion 2d of the body 2 is pressed against a top surface A4 of the dividing wall portion A2 via a seal member S. Thereby, the through hole A3 is closed. Communication holes 2e are formed in a portion of the bottom wall portion 2d opposed to the through hole A3. The communication holes 2e allow for communication between the through hole A3 and an inside of the body 2, thereby allowing for communication between the portion of the ventilation duct E near the outside 0 and the inside of the body 2. The inside of the body 2 is communicated with the inside I via ventilation holes 3b (refer to FIGS. 4 and 5) formed in the cover lid 3. Therefore, the outside 0 and the inside I are communicated with each other via the portion of the ventilation duct E closer to the outside 0 than the dividing wall portion A2, the through hole A3, the communication holes 2e, an inner space of the body 2 and the ventilation holes 3b. Accordingly, the portion of the ventilation duct E near the inside I is substantially composed of the communication holes 2e, the inner space of the body 2 and the ventilation holes 3b. The communication holes 2e, the inner space of the body 2 and the ventilation holes 3b constitute a ventilation passage 5 in the body 2. [0020] As mentioned above, the communication holes 2e are a part of the ventilation passage 5 and a part of the ventilation duct E. By opening and closing the communication holes 2e, the ventilation passage 5 and the ventilation duct E can be opened and closed. And then, the communication between the outside 0 and the inside I can be switched between an opened up state and a shut off state. In other words, the exchange of air between the outside 0 and the inside I can be switched between an stopped state and a ventilating state. The communication holes 2e are opened and closed by an opening-closing member 6. [0021] As shown in FIGS. 5, 6, 8 and 9, the opening-closing member 6 has a configuration of a hollow plate and is received inside the body 2. The opening closing member 6 is horizontally disposed with a longitudinal direction thereof oriented to a longitudinal direction of the body 2. Moreover, the opening-closing member 6 is disposed such that the opening-closing member 6 is movable in the longitudinal direction of the body 2, i.e. in the left-right direction and movable in the vertical direction. The opening-closing member 6 is movable between a first position shown in FIG. 7A and a second position shown in FIG. 7B in the left-right direction and movable between a lower position (closing position) shown in FIG. 7A and FIG. 8 and an upper position (opening position) shown in FIG. 7B and FIG. 9 in the vertical direction. As will be described later, when the opening-closing member 6 is moved rightward (first direction) in FIGS. 7A and 7B from the second position to the first position, the opening-closing member 6 is moved from the upper position to the lower position by a first cam mechanism 8. Conversely, when the opening-closing member 6 is moved leftward (second direction) in FIGS. 7A and 7B from the first position to the second position, the opening-closing member 6 is moved from the lower position to the upper position by a second cam mechanism 9. [0022] A seal member 61 made of an elastic material such as relatively hard rubber is disposed at a bottom surface of the opening-closing member 6. When the opening closing member 6 is positioned at the lower position, the seal member 61 is pressed against a top surface (first reference portion) 2f of the bottom wall portion 2d of the body 2. Moreover, the seal member 61 is disposed such that the seal member 61 surrounds the communication holes 2e when the opening-closing member 6 is at the lower position. Accordingly, when the opening-closing member 6 is positioned at the lower position, the communication holes 2e are closed by the opening-closing member 6, thereby closing the ventilation passage 5. As a result, the communication between the outside 0 and the inside I is shut off by the ventilator 1, and the exchange of air between the outside 0 and the inside I is stopped. Conversely, when the opening-closing member 6 is positioned at the upper position, the opening-closing member 6 and the seal member 61 are spaced upward from the top surface 2f of the bottom wall portion 2d. Thereby, the communication holes 2e are opened, and the ventilation passage 5 is opened. As a result, the communication between the outside O and the inside I is opened up via the ventilation duct E and the ventilation passage 5, and the air is exchanged between the outside 0 and the inside I. [0023] The opening-closing member 6 is moved in the left-right direction by a movement mechanism 7. As shown in FIG. 7A and FIG. 7B, the movement mechanism 7 includes a lever box 71, a lever 72, a link bar 73 and a connecting member 74. [0024] The lever box 71 is composed of a pair of box half bodies 71A, 71B. The pair of box half bodies 71A, 71B are disposed at a left end portion of the inside of the body 2. One of the box half bodies 71A is disposed closer to the outside 0 and the other of the box half bodies 71B is disposed closer to the inside I. The box half bodies 71A, 71B are contacted with each other in a central portion of the body 2 in the inside-outside direction. The box half bodies 71A, 71B are formed so as to be symmetrical with respect to a line dividing the body 2 into two equal parts closer to the outside 0 and closer to the inside I. Therefore, only the one of the box half bodies 71A will be described below. Components of the other of the box half bodies 71B similar to those of the one of the box half bodies 71A will be referred to by the same reference numerals and the description thereof will be omitted. [0025] As shown in FIG. 10, a first guide groove 71a extending in a circular arc configuration is formed in a surface of the box half body 71A opposed to the other box half body 71B. The first guide groove 71a extends along a circular arc. As shown in FIG. 7A and FIG. 7B, the lever 72 is disposed between the pair of box half bodies 71A, 71B. As shown in FIG. 11, guide portions 72a, 72a extending in circular arc configurations are respectively formed in a side surface of the lever 72 facing the outside 0 and a side surface of the lever 72 facing the inside I. One of the guide portions 72a is fitted to the first guide groove 71a of the box half body 71A such that the guide portion 72a is movable in a longitudinal direction of the first guide groove 71a and the other of the guide portions 72a is fitted to the first guide groove 71a of the box half body 71B such that the other guide portion 72a is movable in a longitudinal direction of the first guide groove 71a. Thereby, the lever 72 is disposed at the lever box 71 such that the lever 72 is rotatable in the vertical direction. [0026] The lever 72 is rotatable between an off position shown in FIG. 7A and an on position shown in FIG. 7B. The off position of the lever 72 is determined by the lever 72's abutment against an upper end surface of a positioning protrusion 71b formed in the box half body 71A. A mechanism for determining the on position of the lever 72 will be described later. [0027] A second guide groove 71c is formed in a surface of the box half body 71A opposed to the other box half body 71B. The second guide groove 71c extends horizontally in the left-right direction. As shown in FIG. 7A and FIG. 7B, link bars 73, 73 are respectively disposed at the box half bodies 71A, 71B. The link bars 73, 73 are respectively disposed along the surfaces of the box half bodies 71A, 71B opposed to each other. A protrusion 73a is formed in a surface of one of the link bars 73 opposed to the box half body 71A. The protrusion 73a is disposed in the second guide groove 71c such that the protrusion 73a is movable in the left-right direction but immovable in the vertical direction. Thereby, the one of the link bars 73 is disposed at the box half body 71A such that the link bar 73 is movable in the left right direction but immovable in the vertical direction. Similarly, the other of the link bars 73 is disposed at the box half body 71B such that the link bar 73 is movable in the left-right direction but immovable in the vertical direction. [0028] A first elongated hole 73b is formed in a generally central portion of the link bar 73 in a longitudinal direction thereof. The first elongated hole 73b is oriented such that a longitudinal direction thereof is oriented in the vertical direction. A lower end portion of the lever 72 is disposed between the link bars 73, 73. Protrusions 72b, 72b are respectively formed in opposite side surfaces of the lower end portion of the lever 72 opposed to the link bars 73, 73. The protrusions 72b, 72b are respectively disposed in the first elongated holes 73b, 73b of the link bars 73, 73. Moreover, the protrusion 72b is disposed in the first elongated hole 73b such that the protrusion 72b is movable in the vertical direction but immovable in the left-right direction. Therefore, when the link bar 73 is rotated in the vertical direction, the link bar 73 is moved in the left-right direction in response to the rotation of the link bar 73. [0029] A dividing wall portion 71d protruded toward the box half body 71B is formed in the surface of the box half body 71A opposed to the box half body 71B. The dividing wall portion 71d extends horizontally leftward from a lower end portion of the positioning protrusion 71b to a left end wall of the box half body 71A. Accordingly, a recess 71C is formed in a portion of a top surface of the lever box 71 located to the left of the positioning protrusion 71b. When the lever 72 is in the off position, a left end portion of the lever 72 enters an upper portion of a right end portion of the recess 71C. Therefore, a finger can be inserted in a left end portion of the recess 71C to lift the left end portion of the lever 72 upward. This causes the lever 72 to be rotated from the off position to the on position. It is to be understood that the lever 72 can be rotated from the on position to the off position by pressing down the left end portion of the lever 72. [0030] A left end portion of the link bar 73 is disposed under the dividing wall portion 71d such that the link bar 73 is movable in the left-right direction. A spring bracket 75 is disposed on the left end portion of the link bar 73. An engagement spring 76 having a convex configuration is disposed in the spring bracket 75. As shown in FIG. 7A, when the lever 72 is at the off position, a convex portion 76a of the engagement spring 76 is abutted against a lower end portion of a right end surface (portion where the right end surface and a bottom surface intersect with each other) of the positioning protrusion 71b, and the engagement spring 76 biases the link bar 73 rightward via the spring bracket 75. As a result, the lower end portion of the lever 72 is pressed rightward by the link bar 73, thereby causing the lever 72 to be rotationally biased in a direction from the on position to the off position (counter-clockwise direction in FIGS. 7A and 7B). This rotationally biasing force causes the lever 72 to be pressed against a top surface of the positioning protrusion 71b and to be maintained at the off position. [0031] When the lever 72 is rotated from the off position toward the on position, the link bar 73 is moved leftward. This causes the convex portion 76a to be pressed downward by the positioning protrusion 71b. As a result, the engagement spring 76 is elastically deformed such that a height of the convex portion 76a is reduced. When the lever 72 is rotated further toward the on position, the convex portion 76a is moved past the right end surface of the positioning protrusion 71b and pressed against the bottom surface of the positioning protrusion 71b. Then, the convex portion 76a is slidingly moved past the bottom surface of the positioning protrusion 71b and then slidingly moved on a horizontal bottom surface of the dividing wall portion 71d that continues from the bottom surface of the positioning protrusion 71b. As shown in FIGS. 7A and 7B, an engagement recess 71e is formed in the bottom surface of the dividing wall portion 71d. The engagement recess 71e is disposed such that when the lever 72 is rotated in a direction from the off position to the on position and reaches the on position, the convex portion 76a of the engagement spring 76 is engaged with the engagement recess 71e by an elasticity of the engagement spring 76. In other words, the on position of the lever 72 is determined by the engagement of the convex portion 76a with the engagement recess 71e. [0032] The lever 72 could be rotated further beyond the on position by the elastic deformation of the engagement spring 76 such that the height of the convex portion 76a is reduced. However, immediately after the lever 72 is moved beyond the on position, the protrusion 72b is abutted against an upper end portion of an inner surface of the first elongated hole 73b, and the rotation of the lever 72 is prohibited. Therefore, the lever 72 actually cannot be rotated beyond the on position. [0033] A second elongated hole 73c is formed in a right end portion of the link bar 73. The second elongated hole 73c is oriented such that a longitudinal direction thereof is oriented in the vertical direction. A right end portion of the connecting member 74 is fixed to a left end portion of the opening-closing member 6. A left end portion of the connecting member 74 is disposed between the right end portions of the link bars 73, 73. Protrusions 74a, 74a are respectively formed in opposite side surfaces of the connecting member 74 opposed to the link bars 73, 73. The protrusions 74a, 74a are respectively disposed in the second elongated holes 73c, 73c of the link bars 73, 73. The protrusion 74a is movable in the vertical direction but immovable in the left-right direction with respect to the second elongated hole 73c. Accordingly, when the link bar 73 is moved in the left-right direction, the opening closing member 6 is moved together with the link bar 73. Therefore, when the lever 72 is rotated in the direction from the on position to the off position, the opening closing member 6 is moved rightward (first direction). The position of the opening closing member 6 when the lever 72 reaches the off position is the first position. Conversely, when the lever 72 is rotated in the direction from the off position to the on position, the opening-closing member 6 is moved leftward (second direction). The position of the opening-closing member 6 when the lever 72 reaches the on position is the second position. [0034] When the opening-closing member 6 is moved rightward from the second position to the first position, the opening-closing member 6 is moved downward from the upper position (opening position) shown in FIG. 7B to the lower position (closing position) shown in FIG. 7A by the first cam mechanism 8. Conversely, when the opening-closing member 6 is moved leftward from the first position to the second position, the opening-closing member 6 is moved upward from the lower position to the upper position by the second cam mechanism 9. The first cam mechanisms 8 and the second cam mechanism 9 are disposed between the body 2 and the opening closing member 6 as will be described below. [0035] As shown in FIGS. 5 and 6, two pairs of cam blocks 10, 10' are disposed inside the body 2. One pair of cam blocks 10, 10' are located at the same location in the left-right direction, but spaced from each other in the inside-outside direction such that one is located closer to the outside 0 and the other is located closer to the inside I. One pair of cam blocks 10, 10' and the other pair of cam blocks 10, 10' are spaced from each other in the left-right direction. Only one pair of cam blocks 10, 10' may be disposed or more than two pairs of cam blocks 10, 10' may be disposed. [0036] The cam blocks 10, 10' are mirror symmetrically formed with respect to the body 2. Therefore, only the cam block 10 will be described below and description of the cam block 10' will be omitted. Components of the cam block 10' same as those of the cam block 10 will be referred to by the same reference numerals. [0037] As shown in FIGS. 14 to 17, in a surface of the cam block 10 (disposed closer to the outside 0) opposed to the cam block 10' (disposed closer to the inside I), i.e., the surface of the cam block 10 facing the inside I, a protruded portion 11 protruded toward the other cam block 10' is formed. [0038] A first inclined surface 12 is formed in a left end portion of the protruded portion 11. The first inclined surface 12 is inclined downward from left to right. [0039] A first horizontal surface 13 extending horizontally is formed in the left end portion of the protruded portion 11. The first horizontal surface 13 continues from an upper end portion of the first inclined surface 12. A first spring receiving surface (second reference portion) 14 extends from a left end portion of the first horizontal surface 13 diagonally left up with a small inclination angle. The inclination angle of the first spring receiving surface 14 is smaller than an inclination angle of the first inclined surface 12. Normally, the inclination angle of the first spring receiving surface 14 is designed to be around 5 degrees while the inclination angle of the first inclined surface 12 is designed to be around 30 degrees. While the first horizontal surface 13 is formed continuously from the first inclined surface 12, alternatively, the first horizontal surface 13 may be formed spaced from the first inclined surface 12 to the left as long as the spaced distance is slight. Similarly, the first spring receiving surface 14 may be spaced from the first horizontal surface 13 to the left. [0040] A first relief surface 15 is formed in the left end portion of the protruded portion 11. The first relief surface 15 is formed continuously from a lower end portion of the first inclined surface 12 via a step 16 and a circular arcuate portion 17. The first relief surface 15 extends rightward from the first inclined surface 12. The first relief surface 15 maybe formed continuously from the first inclined surface 12 via the circular arcuate portion 17 in a smooth manner without the step 16 being formed. [0041] A first slit 18 and a second slit 19 are formed to the left of the protruded portion 11. The first slit 18 is disposed along a central portion of the first inclined surface 12. A portion of the first slit 18 divides the first inclined surface 12 into an upper left portion and a lower right portion. The first inclined surface 12 may be a continuous surface in an entirety thereof. A catch protrusion 18a is formed in a side surface of the first slit 18 opposed to and spaced from the first inclined surface 12. A protruded height of the catch protrusion 18a is generally half a width of the first slit 18. The second slit 19 extends along the upper end portion of the first inclined surface 12, the first horizontal surface 13 and the first spring receiving surface 14. [0042] A second inclined surface 22 is formed in a right end portion of the protruded portion 11. The second inclined surface 22 is inclined upward from right to left. An inclination angle of the second inclined surface 22 with respect to a horizontal line is the same as the inclination angle of the first inclined surface 12. Accordingly, the second inclined surface 22 is parallel to the first inclined surface 12. [0043] A second horizontal surface 23 extending horizontally to the right from a lower end portion of the second inclined surface 22 is formed in the right end portion of the protruded portion 11. A second spring receiving surface 24 extends from a right end portion of the second horizontal surface 23 diagonally right down with a small inclination angle. The inclination angle of the second spring receiving surface 24 is the same as the inclination angle of the first spring receiving surface 14. While the second horizontal surface 23 is formed continuously from the second inclined surface 22, alternatively, the second horizontal surface 23 may be formed spaced from the second inclined surface 22 to the right as long as the spaced distance is slight. Similarly, the second spring receiving surface 24 may be spaced from the second horizontal surface 23 to the right. [0044] A second relief surface 25 is formed in the right end portion of the protruded portion 11. The second relief surface 25 is formed continuously from an upper end portion of the second inclined surface 22 via a step 26 and a circular arcuate portion 27. The second relief surface 25 extends leftward from the second inclined surface 22. The second relief surface 25 maybe formed continuously from the second inclined surface 22 via the circular arcuate portion 27 in a smooth manner without the step 26 being formed. [0045] A third slit 28 and a fourth slit 29 are formed to the right of the protruded portion 11. The third slit 28 is disposed along a central portion of the second inclined surface 22. A portion of the third slit 28 is divides the second inclined surface 22 into an upper left portion and a lower right portion. The second inclined surface 22 may be a continuous surface in an entirety thereof. A catch protrusion 28a is formed in a side surface of the third slit 28 opposed to and spaced from the second inclined surface 22 diagonally left down. A protruded height of the catch protrusion 28a is generally half a width of the third slit 28. The fourth slit 29 extends along the upper end portion of the second inclined surface 22, the second horizontal surface 23 and the second spring receiving surface 24. [0046] The first inclined surface 12 and the second inclined surface 22 are generally point symmetric: namely, the first horizontal surface 13 and the second horizontal surface 23 are point symmetric; the first spring receiving surface 14 and the second spring receiving surface 24 are point symmetric; and the first relief surface 15 and the second relief surface 25 are point symmetric. However, the second horizontal surface 23 and the second spring receiving surface 24 are arranged so as to be located slightly lower than the first horizontal surface 13 and the first spring receiving surface 14 when the second horizontal surface 23 and the second spring receiving surface 24 are rotated through 180 degrees, and corresponding to this feature, a length of the first inclined surface 12 is greater than a length of the second inclined surface 22. [0047] A first plate 31 made of metal and a second plate 41 made of metal are disposed in the cam block 10. As shown in FIGS. 18A and 18B, the first plate 31 includes a first plate portion 3 1a having a flat plate configuration, a second plate portion (extension portion) 31b formed continuously from a one end portion of the first plate portion 31a and a third plate portion (elastic portion) 31c formed continuously from the other end portion of the first plate portion 31a. A circular arcuate portion 31d is formed between the first plate portion 31a and the second plate portion 31b so as to smoothly connect the first plate portion 31a and the second plate portion 3lb. A circular arcuate portion 3le is formed between the first plate portion 3 1a and the third plate portion 3 1c so as to smoothly connect the first plate portion 3 1a and the third plate portion 3 1c. [0048] The second plate portion 3 lb and the third plate portion 3 1c are inclined with respect to the first plate portion 31 a. Specifically, the second plate portion 3 lb and the third plate portion 3 1c are inclined with respect to the first plate portion 3 la such that the second plate portion 3 lb and the third plate portion 3 1c extend in opposite directions in a thickness direction of the first plate portion 3 la. An inclination angle of the second plate portion 3 lb with respect to the first plate portion 31 a and an inclination angle of the third plate portion 31c with respect to the first plate portion 31a are the same. The second plate portion 3lb and the third plate portion 31c are parallel to each other. However, it is not required that the inclination angle of the second plate portion 3lb and the inclination angle of the third plate portion 31c are the same, and the former may be smaller than the latter. For example, the inclination angle of the second plate portion 3lb may be generally the same as or slightly greater than the inclination angle of the first spring receiving surface 14. The inclination angle of the third plate portion 31c is designed to be generally a half of the inclination angle of the first inclined surface 12. [0049] A first engagement protrusion 31f is formed in one side of the first plate portion 3la. An engagement hole 31g is formed through a central portion of the first engagement protrusion 31f. A second engagement protrusion 31h is formed in one side surface of an area that extends from one end portion of the first plate portion 31a to a distal end of the second plate portion 3lb. The first engagement protrusion 31f is disposed in the first slit 18 and the second engagement protrusion 31h is disposed in the second slit 19. Moreover, the catch protrusion 18a is fitted in the engagement hole 31g of the second engagement protrusion 31h. In this way, the first plate 31 is fixed to the cam block 10. Moreover, an elasticity of the first plate 31 causes the first plate portion 3 1a to be pressed against the first inclined surface 12 and the second plate portion 3 lb to be pressed against the first spring receiving surface 14. A lower end portion of the first plate portion 31a and the circular arcuate portion 31e and the third plate portion 31c continuing from the lower end portion of the first plate portion 3 1 a are spaced downward from the first relief surface 15. Accordingly, the circular arcuate portion 3 1e and the third plate portion 3 Ic can be elastically deformed such that distal end portions thereof (right end portions thereof) is moved in the vertical direction. [0050] The second plate 41 has a same configuration as the first plate 31. The second plate 41 includes a first plate portion 41a, a second plate portion 41b, a third plate portion 41c, a circular arcuate portion 41d, and a circular arcuate portion 41e, respectively corresponding to the first plate portion 31a, the second plate portion 3 1b, the third plate portion 3 Ic, the circular arcuate portion 3 Id and the circular arcuate portion 31 e of the first plate 3 1. Moreover, corresponding to the disposition of the first plate 31 along the first inclined surface 12, the first horizontal surface 13, the first spring receiving surface 14 and the first relief surface 15, the second plate 41 is disposed along the second inclined surface 22, the second horizontal surface 23, the second spring receiving surface 24 and the second relief surface 25. The second horizontal surface 23 and the second spring receiving surface 24 are located at locations respectively lower than locations where the first horizontal surface 13 and the first spring receiving surface 14 would be if rotated through 180 degrees by predetermined distances. Correspondingly, the second plate 41 is located at a location lower than a location where the first plate 31 would be if rotated through 180 degrees by a predetermined distance. A first engagement protrusion 41f, an engagement hole 41g and a second engagement protrusion 41h respectively corresponding to the first engagement protrusion 3 If, the engagement hole 3 Ig and the second engagement protrusion 3 1h of the first plate 31 are formed in the second plate 41. The first engagement protrusion 41f and the second engagement protrusion 41h are respectively disposed in the third slit 28 and the fourth slit 29 and the catch protrusion 28a is fitted in the engagement hole 41g. [0051] As shown in FIGS. 6, 8 and 9, two pairs of a first abutment portion 51 and a second abutment portion 52 are disposed in a side of the opening-closing member 6 facing the outside 0. The pair of the first abutment portion 51 and the second abutment portion 52 are located at the same location in the vertical direction, but spaced from each other in the left-right direction by a predetermined distance. One pair of the first abutment portion 51 and the second abutment portion 52 and the other pair of the first abutment portion 51 and the second abutment portion 52 are spaced from each other in the left-right direction by a predetermined distance. The first abutment portion 51 and the second abutment portion 52 respectively constitute the first cam mechanism 8 and the second cam mechanism 9 together with the first inclined surface 12, the second inclined surface 22 and some other components of the cam blocks 10. [0052] Two pairs of a first abutment portion 51' and a second abutment portion 52' are disposed in a side of the opening-closing member 6 facing the inside I. The first abutment portion 51' and the second abutment portion 52' respectively constitute the first cam mechanism 8 and the second cam mechanism 9 together with the first inclined surface 12, the second inclined surface 22 and some other components of the cam blocks 10'. The pairs of the first abutment portion 51' and the second abutment portion 52' have same features as the pairs of the first abutment portion 51 and the second abutment portion 52. Therefore, only the first abutment portion 51 and the second abutment portion 52 will be described below and the description of the first abutment portion 51' and the second abutment portion 52' will be omitted. [0053] As shown in FIGS. 14 to 16, the distance between a right end surface of the first abutment portion 51 and a left end surface of the second abutment portion 52 is generally the same as or slightly longer than a distance between a left surface of the first plate portion 3 1a and a right surface of the first plate portion 41a in the left-right direction. Accordingly, when the first abutment portion 51 is abutted against the first plate portion 3 1a, the second abutment portion 52 is generally contacted with or slightly spaced from the first plate portion 41a. Conversely, when the second abutment portion 52 is abutted against the first plate portion 41a, the first abutment portion 51 is generally contacted with or slightly spaced from the first plate portion 31a. [0054] The first abutment portion 51 and the second abutment portion 52 are disposed further to satisfy the following requirements. As depicted in the solid line in FIG. 16 (or as shown in FIG. 14), when the opening-closing member 6 is at the first position, a right end portion of the first abutment portion 51 is abutted against the third plate portion 3 1 c of the first plate 31 to move a right end portion of the third plate portion 3 1c upward, thereby the third plate portion 3 1c and the circular arcuate portion 31e being elastically deformed. As a result, the first abutment portion 51 is biased downward by the third plate portion 31c. On the other hand, the second abutment portion 52 is opposed to the third plate portion 41c of the second plate 41 but is spaced from any portion of the third plate portion 41c when the opening-closing member 6 is at the first position. [0055] As mentioned above, when the opening-closing member 6 is at the first position, the first abutment portion 51 is biased downward by the third plate portion 3 1c and the second abutment portion 52 is spaced from the third plate portion 41c. Accordingly, the opening-closing member 6 is biased downward by an elastic force of the third plate portion 3 1c and pressed against the top surface 2f of the bottom wall portion 2d via the seal member 61. Therefore, the communication holes 2e are closed (the ventilation passage 5 is closed) by the opening-closing member 6, and thereby, the ventilation duct E is closed by the ventilator 1. As a result the exchange of air between the outside 0 and the inside I is stopped. The position of the opening closing member 6 when the opening-closing member 6 is pressed against the bottom wall portion 2d via the seal member 61 is the lower position (closing position). The opening-closing member 6 is maintained at the lower position by a biasing force of the third plate portion 3 1c. [0056] The first abutment portion 51 and the second abutment portion 52 are disposed further to satisfy the following requirements. As depicted in the imaginary line in FIG. 16 (or as shown in FIG. 15), when the opening-closing member 6 is at the second position, a left end portion of the second abutment portion 52 is abutted against the third plate portion 41c of the second plate 41 to move a right end portion of the third plate portion 41c downward, thereby the third plate portion 41c and the circular arcuate portion 41e being elastically deformed. As a result, the second abutment portion 52 is biased upward by the third plate portion 41c, and thereby, the opening-closing member 6 is biased upward. On the other hand, the first abutment portion 51 is located below the second plate portion 3 lb of the first plate 31 and is pressed against the second plate portion 3 lb by a biasing force of the third plate portion 41c biasing the opening-closing member 6 upward. Specifically, the first abutment portion 51 is pressed against a portion of the second plate portion 31b located immediately below an intersecting portion where the first horizontal surface 13 and the first spring receiving surface 14 intersect with each other. Alternatively, the first abutment portion 51 may be pressed against a portion of the second plate portion 3 lb that is opposed only to the first spring receiving surface 14 or a portion of the second plate portion 31b that is opposed only to the first horizontal surface 13. [0057] As mentioned above, when the opening-closing member 6 is at the second position, the first abutment portion 51 is pressed against the first spring receiving surface 14 via the second plate portion 3 lb and the opening-closing member 6 is maintained at a certain position in the vertical direction. The position of the openingclosing member 6 at this time is the upper position. The first abutment portion 51 may be pressed against the first horizontal surface 13 via the second plate portion 3 lb when the opening-closing member 6 is at the second position. When the opening closing member 6 is at the upper position, the seal member 61 is spaced upward from the bottom wall portion 2d and the communication holes 2e are open. Accordingly, the communication between the portion of the ventilation duct E closer to the outside o and the portion of the ventilation duct E closer to the inside I is open via the ventilation passage 5 of the ventilator 1, and the air is exchanged between the outside o and the inside I. [0058] As shown in FIGS. 2, 4 and 5, an operation window 3c is formed in the cover lid 3. The operation window 3c is disposed so as to be opposed to an upper end portion of the lever 72 and the recess 71C of the lever box 71. Accordingly, when the lever 72 is at the off position, a finger can be inserted through the operation window 3c to lift the left end portion of the lever 72 upward. This causes the lever 72 to be rotated from the off position to the on position. The lever 72 at the on position can be rotated to the off position by pressing down the left end portion of the lever 72. [0059] In the ventilator 1 having the features as mentioned above, let us assume that the lever 72 is at the off position. At this time, the opening-closing member 6 is at the first position in the left-right direction and at the lower position in the vertical direction. The opening-closing member 6 is pressed against the top surface 2f of the bottom wall portion 2d by the elastic force of the third plate portion 31c of the first plate 31 via the seal member 61. Accordingly, the ventilation passage 5 is closed and the exchange of air between the outside 0 and the inside I is stopped. Moreover, since the opening-closing member 6 is pressed against the bottom wall portion 2d, the opening-closing member 6 will not wobble. Particularly, even if there are dimension errors in the body 2, the cam blocks 10, 10' or the opening-closing member 6 that may affect positional accuracy of the opening-closing member 6 in the vertical direction, such dimension errors may be absorbed by the elastic deformation of the third plate portion 31c of the first plate 31. Therefore, the opening-closing member 6 is securely pressed against the bottom wall portion 2d via the seal member 61. Thus, the opening-closing member 6 can be prevented from wobbling and the communication holes 2e can be securely closed by the opening-closing member 6. Moreover, the seal member 61 is not pressed against the bottom wall portion 2d with an excessive amount of force, and therefore, early deterioration of the seal member 61 can be avoided. [0060] When the lever 72 is rotated from the off position toward the on position, the opening-closing member 6 is moved leftward from the first position toward the second position. When the opening-closing member 6 is moved through a predetermined distance, the second abutment portion 52 is abutted against the second inclined surface 22 via the first plate portion 41a. On the other hand, the first abutment portion 51 is slightly spaced leftward from or simply contacted with the first plate 3 1. Accordingly, when the lever 72 is rotated further toward the on position and the opening-closing member 6 is moved further to the left, the second abutment portion 52 is slid on the first plate portion 41a. Since the first plate portion 41a is made of metal, the second abutment portion 52 can be slid more smoothly compared to when the second abutment portion 52 is slid directly on the second inclined surface 22 and abrasion of the second inclined surface 22 can be prevented. [0061] When the second abutment portion 52 is slid on the first plate portion 41a, the second abutment portion 52 is moved upward by a camming action of the second inclined surface 22 (first plate portion 41a), and thereby, the opening-closing member 6 is moved upward. As is clear from this, the second inclined surface 22 and the first plate portion 41a constitute a second cam part and the second cam part and the second abutment portion 52 constitute the second cam mechanism 9. [0062] When the lever 72 is rotated further toward the on position and the opening closing member 6 is moved further toward the second position accompanying the rotation of the lever 72, the second abutment portion 52 is moved past the first plate portion 41a and abutted against the circular arcuate portion 41e. Then, accompanying the movement of the opening-closing member 6, the second abutment portion 52 elastically deforms the circular arcuate portion 41e such that a distal end portion of the third plate portion 41c is moved downward. Then, when the opening-closing member 6 is moved even further toward the second position, the second abutment portion 52 is abutted against the third plate portion 41c and continues to elastically deform the third plate portion 41c. As a result, the second abutment portion 52 is biased upward, and thereby, the opening-closing member 6 is biased upward. When the second abutment portion 52 is slid on the circular arcuate portion 41e and the third plate portion 41c, the first abutment portion 51 is slid on the circular arcuate portion 31d and on the second plate portion 31b. When the opening-closing member 6 reaches the second position, the first abutment portion 51 is pressed against the first spring receiving surface 14 via the second plate portion 31b by an elastic force of the third plate portion 41c. The position of the opening-closing member 6 in the vertical direction at this time is the upper position (opening position). When the opening closing member 6 is at the upper position, the opening-closing member 6 is securely maintained at the upper position without wobbling because the first abutment portion 51 is pressed against the first spring receiving surface 14 via the second plate portion 3 lb. [0063] As is clear from the above, in this embodiment, the circular arcuate portion 41e and the third plate portion 41c act as a second biasing mechanism that biases the opening-closing member 6 upward (in a direction from the closing position to the opening position). However, it is not necessary that the circular arcuate portion 41e and the third plate portion 41c act as the second biasing mechanism. Instead, only the third plate portion 41c may act as the second biasing mechanism. Alternatively, the third plate portion 41c and a portion of the circular arcuate portion 41e that continues from the third plate portion 41c may act as the second biasing mechanism. In the former case, the entirety of the circular arcuate portion 41e serves as a part of the second cam part. In the latter case, the remaining portion of the circular arcuate portion 41e (portion that continues from the first plate portion 41a) serves as a part of the second cam part. Alternatively, the entirety of the circular arcuate portion 41e may be used as the part of the second cam part or as a part of a second elastic portion (the second biasing mechanism). In this embodiment, the first spring receiving surface 14 serves as the second reference portion for determining the upper position (opening position) of the opening-closing member 6. Alternatively, the second plate portion 3 lb may be contacted with the first horizontal surface 13 so that the first abutment portion 51 is abutted against the first horizontal surface 13 via the second plate portion 3 lb when the opening-closing member 6 is at the second position (upper position). In this case, the first horizontal surface 13 serves as the second reference portion. [0064] When the lever 72 positioned at the on position is rotated toward the off position, the opening-closing member 6 is moved rightward from the second position toward the first position. When the opening-closing member 6 is moved from the second position through a predetermined distance, the first abutment portion 51 is abutted against the first inclined surface 12 via the first plate portion 3 1a of the first plate 31. On the other hand, the second abutment portion 52 is slightly spaced rightward from or simply contacted with the second plate 41. Accordingly, when the lever 72 is rotated further toward the off position and the opening-closing member 6 is moved further to the right, the first abutment portion 51 is slid on the first plate portion 31a. Since the first plate portion 31a is made of metal, the first abutment portion 51 can be slid more smoothly compared to when the first abutment portion 51 is slid directly on the first inclined surface 12 and abrasion of the first inclined surface 12 can be prevented.
[0065] When the first abutment portion 51 is slid on the first plate portion 31a, the first abutment portion 51 is moved downward by a camming action of the first inclined surface 12 (first plate portion 3 1a), and thereby, the opening-closing member 6 is moved downward. As is clear from this, the first inclined surface 12 and the first plate portion 3 1a constitute a first cam part and the first cam part and the first abutment portion 51 constitute the first cam mechanism 8. [0066] When the lever 72 is rotated further toward the off position and the opening closing member 6 is moved further toward the first position accompanying the rotation of the lever 72, the first abutment portion 51 is moved past the first plate portion 31a and abutted against the circular arcuate portion 31e. Then, accompanying the movement of the opening-closing member 6, the first abutment portion 51 elastically deforms the circular arcuate portion 31 e such that a distal end portion of the third plate portion 31c is moved upward. Then, when the opening-closing member 6 is moved even further toward the first position, the first abutment portion 51 is abutted against the third plate portion 3 ic and continues to elastically deform the third plate portion 31c. As a result, the first abutment portion 51 is biased downward, and thereby, the opening-closing member 6 is biased downward. When the first abutment portion 51 is slid on the circular arcuate portion 3 le and the third plate portion 31 c, the second abutment portion 52 is spaced from the second plate 41. Particularly, the second abutment portion 52 is spaced upward from the circular arcuate portion 41d and the second plate portion 41b. When the opening-closing member 6 reaches the second position, the opening-closing member 6 is moved up to the upper position (opening position). [0067] As is clear from the above, in this embodiment, the circular arcuate portion 3 1e and the third plate portion 3 1c act as a first biasing mechanism that biases the opening-closing member 6 downward (in a direction from the opening position to the closing position). However, it is not necessary that the circular arcuate portion 31e and the third plate portion 31c act as the first biasing mechanism. Instead, only the third plate portion 31c may act as the first biasing mechanism. Alternatively, the third plate portion 31 c and a portion of the circular arcuate portion 3 1 e that continues from the third plate portion 31c may act as the first biasing mechanism. In the former case, the entirety of the circular arcuate portion 31e serves as a part of the first cam part. In the latter case, the remaining portion of the circular arcuate portion 31e (portion that continues from the first plate portion 31a) serves as a part of the first cam part. Alternatively, the entirety of the circular arcuate portion 31e may be used as the part of the first cam part or as a part of a first elastic portion (the first biasing mechanism). [0068] The present invention is not limited to the embodiment described above. Various modifications can be made without departing from the scope and spirit of this invention. For example, in the embodiment described above, when the opening-closing member 6 is moved in the left-right direction, the opening-closing member 6 is moved in the vertical direction to open or close the ventilation passage 5. Alternatively, depending on the orientation of the ventilation passage 5, the opening closing member 6 may be moved in the left-right direction to open or close the ventilation passage 5. The body 2 may be disposed such that the top surface of the ventilator 1 (top surface of the cover lid 3) is horizontally oriented toward the inside I. Moreover, in the embodiment described above, when the opening-closing member 6 is moved in the left-right direction, the opening-closing member 6 is moved in the vertical direction by the first cam mechanism 8 and the second cam mechanism 9 respectively disposed at the cam blocks 10, 10'. Alternatively, as with the invention disclosed the Patent Document 1 mentioned above, one side portion of the opening-closing member 6 may be rotatably supported by the body 2 and a cam mechanism may be disposed only between the other side portion of the opening-closing member 6 and the body 2. Moreover, in the embodiment described above, the cam blocks 10, 10' are disposed on the body 2. Alternatively, the cam blocks 10, 10' may be disposed on the opening-closing member 6. In this case, the first abutment portion and the second abutment portion are disposed on the body 2. Alternatively, the cam blocks 10, 10' may be disposed neither on the body 2 nor on the opening-closing member 6. In other words, the cam blocks 10, 10' may be omitted. In this case, the first cam part and the second cam part may be directly disposed in one of the body 2 and the opening-closing member 6, and the first abutment portion 51 and the second abutment portion 52 may be disposed in the other of the body 2 and the opening-closing member 6. Furthermore, while in the embodiment described above, the first inclined surface 12 and the first plate portion 31a of the first plate 31 constitute the first cam part, the first cam part may be composed only of the first inclined surface 12. In this case, in place of the third plate portion 31 c and the circular arcuate portion 3 1 e of the first plate 31, other components acting as the first biasing mechanism are disposed on the body. The same applies to the second cam part and the second biasing mechanism. Industrial Applicability [0069] The ventilator according to the present invention can be installed at a wall or a window or the like of a building and used as a device for exchanging air between the outside and the inside. Reference Numerals [0070] I inside 0 outside 1 ventilator 2 body 2e communication holes (a part of a ventilation passage) 2f top surface (first reference portion) 5 ventilation passage 6 opening-closing member 8 first cam mechanism 9 second cam mechanism 10 cam block 10' cam block 12 first inclined surface (first support portion) 14 first spring receiving surface (second reference portion) 22 second inclined surface (second support portion) 31 first plate 31a first plate portion (first cam part) 31b second plate portion (extension portion) 31c third plate portion (first elastic portion) 3le circular arcuate portion (first elastic portion) 41 second plate 41a first plate portion (second cam part) 41c third plate portion (second elastic portion) 41e circular arcuate portion (second elastic portion)