PURPOSE: To enable proper exposure control through stable measurement by applying a stable voltage to a measuring circuit while stopping the oscillation of a light emitting circuit during flashing.

CONSTITUTION: As transistor 12 conducts through a feedback winding 11b of the oscillating transformer, electric currenet flows through winding 11a to charge main capacitor 17 via diode 14 and when synchro contact 23 coupling with the shutter is closed, discharge tube 24 flashes. With this contact 23 closed, the charge of capacitor 16 flows through protective resistance 15, etc., to turn on transistor 6, and consequently the closed circuit of transistor 6, diode 5, the base electrode of transistor 12, resistance 8, capacitor 7, etc., is formed to stop the oscillation of transformer 11, so that a stable voltage will be applied to phototransistor 9. Therefore, exposure in flash photography is controlled properly by dimming operation according to stable measurement.