PURPOSE: To suppress increase of DC output voltage under light load while suppressing surge current upon turn ON of power.

CONSTITUTION: Capacitors C1, C2 and a diode D2 are connected alternately in series between first and second output terminals T1, T2 and the Joints of the capacitors C1, C2 and the diode D2 are connected alternately through diodes D1, D2 with the output terminal T2, T1 sequentially from the one closer to the first output terminal TL thus constituting nonlinear impedance circuits 10, 10'. Output terminals T1 are connected, respectively, with positive and negative DC output terminals of a diode bridge 20 whereas the output terminals T2 are connected collectively with one end of an AC power supply AC through a triac Trc. When DC output voltage Ed from the diode bridge 20 is higher than a reference voltage Ed*, the triac Trc is opened to disconnect the nonlinear impedance circuits 10, 10' from the AC power supply AC.