Abstract: In the constant-voltage automatic charging strobe circuit (100), the power circuit (20) for driving the automatic exposure mechanism rectifies the AC voltage generated in the collector of the oscillation control transistor (Q1) connected to the primary side of the step-up transformer (T1) to direct current by means of the rectifying diode (D4), smoothes the current by means of the capacitor (C3), and generates a DC secondary source. This DC secondary source is stepped up to a higher voltage than the battery voltage (VB), through the transistor (Q2) that is turned on and off by the phototransistor (PH1) for determining the level of ambient light, and is supplied as the source for driving the aperture control solenoid (RE1).