A light projector and a light receiver each includes a case body, a light transmission plate closing an opening in a front face of the case body, and a pair of caps closing openings in end faces of the case body. The case body includes first supports supporting side edges of the light transmission plate, the caps respectively include second supports supporting ends of the light transmission plate, the light transmission plate is supported by the first supports and the second supports with an elastic member interposed between the light transmission plate and the first and second supports, and the cap is fixed to the case body while the seal member abutting on the end face of the case body is interposed between the cap and the case body. A cured liquid sealing agent is interposed between leading ends of the seal member and the elastic member.