The present invention provides a flash discharging circuit for simplifying the charging of electric power in a capacitor. When energy discharged from a transformer for storing and discharging energy is charged in a main capacitor of the circuit, a detection voltage inputted to a first input terminal of a comparator so as to detect a primary current flowing through a primary winding of the transformer is compared with a reference voltage inputted to a second input terminal of the comparator. According to a result of the comparison, it is detected that a predetermined primary current flows through the primary winding of the transformer. When the primary current flowing through the primary winding of the transformer is turned off, the reference voltage is set to be lower than the detection voltage.