Lens-fitted photo film unit having aperture stop device

A lens-fitted photo film unit is pre-loaded with photo film. A photometric circuit measures object brightness of a photographic object, and determines which of high brightness or low brightness the object brightness is according to comparison with a predetermined reference brightness level. A mode selector in a button shape sets a selected one of an AE mode and a night scene mode. A combination of stationary and movable aperture stop plates changes over a photographic light path in a selected one of small, middle and large aperture stop states. The movable aperture stop plates set the light path in the small aperture stop state when the AE mode is determined and also upon detection of the high brightness. The light path is set in the middle aperture stop state when the AE mode is determined and also upon detection of the low brightness. The light path is set in the large aperture stop state when the night scene mode is determined.