PURPOSE: To suppress voltage rise under light load by conducting current through an inductor even during voltage supply interval from a DC auxiliary power supply to a high frequency converter thereby suppressing distortion in the input current waveform.

CONSTITUTION: During trough interval of output voltage from a rectifier 100 where the instantaneous value is lower than a predetermined level, voltage is fed mainly from an auxiliary DC power supply 6 to an inverter 1. Upon turn ON of a switching device 3, current flows from the rectifier 100 through an inductor (L) 12-a diode (D) 13-the device 3 and energy is stored in the L12. Upon turn OFF of the device 3, power stored in the L12 is discharged through a route of L12-a parallel resonance circuit 2-a low capacity capacitor (C)-the rectifier 100-L12 and the C14 is charged. The C14 is discharged to the inverter 1 upon next turn ON of the device 3 and a C7 is charged via the route of C7-L8-D10-the device 3.