Abstract: In a photoelectric switch comprises a light projecting part, a light receiving part and a control part for controlling these parts. The light projecting part and the light receiving part are fixed in mounting holes in the following manner. The light projecting part and the light receiving part further comprises a cylindrical holder having a flange at one end, a circular truncated cone-type hook sliding on the holder and having a variable diameter, and a spring for pressing this hook toward the flange of the holder. The holder of the light projecting part or the light receiving part is inserted into the mounting hole. With use of a suitable tool, the hook is separated from the flange and the diameter of the large diameter part is momentarily reduced. The hook is penetrated through the mounting hole, and the peripheral part of the mounting hole is held between the large diameter part of the expanded hook and the flange.