PURPOSE: To perform a quick discharge processing through a semiconductor switching element by equipping both ends of a capacitor with a circuit discharging a charged electric load and by issuing a voltage command value lower than a capacitor terminal voltage to cause a capacitor charger and a discharge circuit to cooperate with each other.

CONSTITUTION: A voltage setter 11 sets the desired value of a charging voltage and a charging voltage detector 12 detects the actual value of said charging voltage. When the voltage desired value is set to a value lower than the voltage actual value at the point of time of the completion of charging of a capacitor 5, a signal fixing a conduction angle signal outputted by a phase shifter 14 to the minimum value (substantially, a conduction angle is zero) decided by a limiter is outputted from a voltage regulator 13. When a voltage command value lower than the terminal voltage of said capacitor 5 is outputted, a DC/DC converter 4 discontinues its charging action and a semiconductor switching element 24 is turned ON so that the electric charge of said capacitor 5 is consumed by a discharging resistor 25. Said ON state of the semiconductor switching element 24 continues until the terminal voltage of said capacitor 5 coincides with the voltage command value.