A lens-fitted photo film unit is pre-loaded with photo film, and is a flash built-in type. A booster circuit boosts power source voltage to obtain high voltage. A main capacitor stores charge at the high voltage. A flash discharge tube is connected with the main capacitor, and emits flash light by discharge at the high voltage. A trigger circuit triggers the discharge of the flash discharge tube in response to an exposing operation. A main circuit board has the booster circuit and the trigger circuit mounted thereon. A subsidiary circuit board is connected with the main circuit board, and has a flash quenching circuit mounted thereon. The flash quenching circuit operates in an auxiliary manner, and automatically adjusts the amount of the flash light.