A multi-optical axis photoelectric sensor is provided having a casing that forms an outer shape of each of a projector and an optical receiver. The casing includes a frame body having a front face and two ends opened, a pair of caps to cover both ends of the frame body, and a light transmissive plate to cover the opened front face of the frame body 3. In the inner surfaces of both side plates of the frame body, supports are formed extending along the corresponding side edges of the opening of the front face. Both side edges of the light transmissive plate 6 are supported by the supports, and both ends thereof are supported by the caps. Portions of the caps that support the light transmissive plate 6 include communication portions to communicate with the supports of the frame body 3, and a string-like elastic member is disposed around a closed loop formed by each support and each communication portion. The light transmissive plate 6 is held between the string-like elastic member and at least one fixing member disposed for the frame body and the caps. This configuration facilitates fixing of the light transmissive plate and changing of a size of the frame body.