Lens-fitted photo film unit

A lens-fitted photo film unit pre-loaded with photo film, wherein an exposure is taken through an exposure opening upon depression of a shutter button from an initial, unpressed position to a full depressed position, said lens-fitted photo film unit comprising:

• there being a halfway position in depression of said shutter button, determined between said initial, unpressed position and said full depressed position;
• a power source switch, connected to a power source, and switched on upon movement of said shutter button to said halfway position;
• a photometric circuit for receiving light of an object, and for generating a changeover signal when brightness of said object is a predetermined brightness or more, said photometric circuit being rendered effective when said power switch is switched on;
• a changeover plate having a stop-down opening which is formed therein, and has a size smaller than said exposure opening, said changeover plate being movable between an inserted position and a retracted position, said stop-down opening of said inserted position being superposed on said exposure opening to intercept a periphery of said exposure opening, and said stop-down opening of said retracted position being away from said exposure opening, said changeover plate being in said retracted position while said exposure is taken if said power source is exhausted;
• and
• a stop drive unit for moving only said changeover plate, said stop drive unit setting said changeover plate in said inserted position upon occurrence of said changeover signal and in response to movement of said shutter button to said full depressed position from said halfway position, said stop drive unit setting said changeover plate in said retracted position in absence of said changeover signal, said stop drive unit comprising:
• a first spring for biasing said changeover plate toward said retracted position;
• a retainer member, said retainer member movable as a result of depression of said shutter button, said retainer member holding said changeover plate in said inserted position when said shutter button is in said initial, unpressed position and when said shutter button is in said halfway position;
• said retainer member allowing said changeover plate to be moved by said first spring when said shutter button is in said full depressed position;
• and
• an electromagnet, said electromagnet being connected to said photometric circuit, said electromagnet contacting and holding only said changeover plate in said inserted position against said first spring in response to said changeover signal.