To provide a diaphragm switching device capable of adjusting the exposure without using expensive parts and a large space.

This diaphragm switching device is equipped with a movable diaphragm plate 45 which is provided to freely move between a photographing lens 6 and a shutter blade 42 and where a 1st aperture 67 having a small diameter of opening and a 2nd aperture 66 having a large diameter of opening are formed and a fixed large diaphragm aperture 64a provided behind the plate 45. By moving the plate 45, the aperture 67 is used as the diaphragm of a photographing system when it is set on a photographing optical axis, and the aperture 64a is used as the diaphragm of the photographing system when the aperture 66 is set on the photographing optical axis. Then, the plate 45 is used as a flare stopper for intercepting harmful light made incident from the lens 6 and going toward the outside of a harmful exposure range on film.