To provide a lens-fitted photographic film unit which is provided with an inexpensive diaphragm switching device with a one-constitution photographing lens combined.

The photographing lens 5 is held by a lens holder rib 52. An aperture 51 as an open diaphragm is formed behind the lens holder rib 52. A diaphragm plate 42 is arranged behind the photographing lens 5, and a diaphragm aperture 61 formed in the plate 42. A notched part 52a is formed in the lens holder rib 52. The leading end part of the diaphragm plate 42 is inserted from the notched part 52a and a small diaphragm aperture 61 is positioned on a photographing optical path. As a switching plate 38 is slid and moved upward, a switching piece 39 pushes an abutting piece 62c downward, then, the diaphragm plate 42 is turned, and the diaphragm plate 42 is moved outside the lens holder rib 52 from the notched part 52a, and the small diaphragm aperture 61 is retreated from the photographing optical path.