PURPOSE: To prevent over-exposure at a short-distance side by varying the dimming level of an auto stroboscope according to the photographic distance.

CONSTITUTION: A potentiometer 2 is coupled with a photographic lens which is operated manually, and a voltage is inputted as the dimming level to a comparator 4. Reflected light from a subject is inputted to the photodiode 6 of an operational amplifier 5. The output of a capacitor 8 is compared with the dimming level by the comparator 4, which outputs a light emission stop signal to a stroboscope circuit 10 when they coincide with each other to stop a discharge tube 12. The meter 2 generates a voltage corresponding to the photographic distance, and this is sent as the dimming level to the comparator, which compares the input with the terminal voltage of a capacitor 7 integrating the quantity of the reflected light. Therefore, the voltage of the potentiometer 2 is set so that the voltage is low at the short-distance side, thus the quantity of light emission is reduced at the short-distance side to prevent over-exposure.