To automatically select whether stroboscopic light emission is to be done or not in accordance with the luminance of a subject.

A trigger circuit within a stroboscopic circuit consists of a trigger capacitor 51, a trigger coil 52, a synchronous switch 40, a thyristor 57 and a recharging switch 41. The gate terminal of the thyristor 57 is connected to a diaphragm controlling circuit 74 and the plus electrode of a battery 38. The circuit 74 is provided with a photometric section, a diaphragm switching section made of a solenoid and a transistor which turns on and off the thyristor 57. When the luminance of the object is higher than a reference value, the transistor is operated together with the solenoid, the diaphragm is switched to a smaller diaphragm and the thyristor 57 is turned off. Thus, the trigger circuit is shut off and stroboscopic light emission is prohibited. Conversely, when the luminance of the object is equal to or less than the reference value, the solenoid and the transistor are not operated, and the thyristor 57 maintains its on state while the diaphragm is kept open.