PURPOSE: To reduce noise by lowering the peak value of AC sine wave rectified by the chopper action of a semiconductor switching element to 1/2 and less and by alternately charging two capacitors with electricity via inductance and outputting therefrom.

CONSTITUTION: The output of AC power supply 1 is rectified by a fullwave rectifier circuit 2 and outputted from terminals 2a∼2b. The reference voltage of a terminal 12 is inputted to operational amplifiers 10a, 10b being comparator circuits, and the output of each junction point of resistors 6a∼7b parallelly- connected with capacitors 5a∼5b is also inputted thereto. When a capacitor- detected voltage exceeds said reference voltage, Trs 3a, 3c are turned OFF by an F circuit 11. Since the Trs 3a, 4a are turned OFF, a magnetic energy stored in inductors 26a, 26b charges said capacitors 5a, 5b via diodes 27a, 27b. Thus, it is possible to obtain DC power supply applying a voltage at the set point corresponding to that of said reference voltage terminal 12 to a load 9.