A resin case (10), which is provided with a condenser lens (61) through which light is transmitted, accommodates a circuit board (31) on which a photoelectric element (33) disposed at the focal point of the condenser lens (61) is mounted. The circuit board (31) has a through hole (31c) through which light that has been transmitted through the condenser lens (61) passes. The photoelectric element (33) is mounted on the rear surface (31b) of the circuit board (31) on the side opposite the condenser lens (61), and receives light which has passed through the through hole (31c).