PURPOSE: To let switch operation be accomplished surely and permit the handling of the switch even in a dark place by specifying the disposition of optical guides and reflectors, make the positions and reflecting angles of the reflectors adjustable and covering the space formed by the reflectors and guide end faces with a transparent film.

CONSTITUTION: The end faces 19, 20 of a pair of optical guides 17, 18 are adjacently disposed at an opening of 90° within a light-shielded box body 11. The 1st reflector 24 is provided in the position where the optical axes of the end faces 19, 20 intersect at 45°. Next, a lever 30 is oscillated by a knob 32 to detach the 1st reflector 24 from the side of a frame 23 and deviate the same from the optical axis of the end face 19 of the optical guide 17. Light enters the 2nd reflector 34, passes through a light-transmittable cover 15 and is radiated to the outside of the photo switch from the window 16, thereby turning off the photo switch. The space 25 formed by the optical guide end faces 19, 20 and 1st reflector 24 is covered with a transparent film 26 to prevent the malfunction by the effect of water, steam and gas and permit easy handling of the switch by the light radiated to the outside even in a dark place.