Photo detection device

The invention provides a photo detection device (100) that can facilitate assembly while realizing miniaturization. The photo detection device comprises an illuminance sensor (1), a microcomputer (2) for controlling a headlight and a taillight based on a detection result of the illuminance sensor, a first printed circuit board (10) on which the illuminance sensor (1) is mounted, a second printed circuit board (20) on which the microcomputer is mounted, a holding member (30) for holding the first and second printed circuit boards, and a housing (50) for accommodating the holding member. The second printed circuit board (20) is arranged in a plane different from a plane in which the first printed circuit board (10) is arranged.