To provide a lens-fitted photographic film unit to effectively prevent improper reuse.

An electronic flash substrate 31 is provided with a heater 42. The heater 42 is connected in series with a power supply battery 33, a resistor R and a switch, and is biased toward a body base 14 with a spring 43. The switch is mounted on a film counter plate 38. After all picture frames are exposed and the film is wound up, the film counter plate 38 rotates and brings a metal chip 39 into contact with two metal chips 40, 41 to turn on the switch to supply a current from the power supply battery 33 to the heater 42. The heater 42 generates heat to deform the body base 14 according to the force by the spring 43. This prevents photographing even if the unit body is loaded with a new photographic film. Even when exchange of the damaged base is attempted, many parts are required to be disassembled and then assembled again. This effectively prevents improper reuse of the unit.