PURPOSE: To prevent serially connected capacitors from being reversely charged by the reflected energy of a load by connecting in parallel a serial circuit constituted of a diode and a resistance with a reactor.

CONSTITUTION: The serial circuit constituted of a diode 11 and a resistance 12 is connected in parallel with a first reactor 6 so that the direction of the diode 11 can block the discharge of a charged voltage at the time of the first charge. First of all, a capacitor 4 and a capacitor 5 are charged in parallel through a switching element 1 and a second reactor 3 by a direct current charging power source 2. At that time, the action of the serial circuit constituted of the diode 11 and the resistance 12 is not at all affected because the diode 11 blocks the voltage. Then, when the voltage acts upon a load resistance 10, and the serial capacitors 4 and 5 are reversely charged by the energy reflected from the load resistance 10, this charge is speedily discharged through the serial circuit constituted of the diode 11 and the resistance 12, so that the residual charge can be removed.