PURPOSE: To project or store automatically a strobe light emission part by generating a difference in brigthness level at which an operation is performed according to the variation state of subject brightness and providing the photometric operation with hysteresis.

CONSTITUTION: When a specific voltage is supplied from a power source terminal 1 while the strobe light emission part is at a storage position, a photocurrent flows through resistances 3 and 4 since a switch 10 is off. A comparator 8 compares the level of the voltage drop generated across the resistances 3 and 4 by the photocurrent with the voltage level of a reference power source 9 to lower the subject brightness; and the voltage drop level drops at hand-shake limit brightness to invert the output from H to L. When the strobe light emission part is moved from the storage part to a projection position to turn on the switch 10, the specific voltage applied to the power source terminal 1 is supplied between the base and emitter of a transistor 7, which turns on to form a short circuit across the resistance 4.