A numerical simulation of a sea-breeze front (SBF) is carried out to investigate the nocturnal frontogenesis (FG) phenomenon that occurs as the SBF propagates inland during the nighttime. At first, we reproduce the FG event of the nighttime SBF based on high-resolution numerical modeling. Then, to reveal its formation mechanism, the FG equation is used, and contributions of each term in the FG equation are estimated for explaining this nocturnal FG event. The results show that the nocturnal FG event of the nighttime SBF: (1) is mostly attributed to the confluence effect due to the horizontal velocity convergence and intensification of the horizontal potential temperature gradient at the front; (2) is partly attributed to the no significant tendency of the turbulence effect associated with the surface cooling.