PURPOSE: To reduce the number of components for securing an element and the number of assembling steps while preventing short-circuit of the leads of element by providing the housing with claws for stopping a light emitting element and a light receiving element, and a mechanism for holding each lead of both elements.

CONSTITUTION: The housing is formed into C-shape having an air gap 31 in the center with case openings 32 for receiving a light emitting element 1 and a light receiving element 2 being provided on the opposite sides thereof. Claws 33 for stopping a PCB are provided on the opposite side faces on the case opening 32 side. The stopping claws 33 prevent floating of the housing 3 and the PCB 4 and engaged, on the engaging face 33a thereof, with the rear surface of the PCB 4. At the time of assemblage, the leads 21 of the light receiving element 2 are inserted through the case opening 32 into lead holding holes and projected to the read side of the PCB 4 through the lead holes 42 thereof before the projected parts of the leads 21 are soldered to the PCB 4 on the rear side thereof.