PURPOSE: To attain the improvement of an input power factor and reduction of higher harmonics of an input current for both a single-phase input and a three-phase input by a method wherein discrimination between these inputs is conducted and a chopper used for the improvement of the input power factor and the reduction of the higher harmonics of the input current at the time of the single-phase input is operated with a control mode changed to a constant- current control at the time of the three-phase input.

CONSTITUTION: A single-phase power supply is inputted to a phase R and a phase T, and a DC voltage signal S is obtained by multiplying an input voltage signal S2 of a rectifier 1 and a deviation voltage signal S2 of an output voltage signal VDC of a chopper 2 from a set voltage VDCSET by a multiplier 13. This DC voltage signal S4 and an output current signal S5 of the rectifier 1 are compared with each other by a hysteresis comparator 14, a square-wave pulse signal S6 is outputted and thereby a transistor 5 of the chopper 2 is ON-OFF controlled so that an input current be in accord with an input voltage in a hysteresis width. At the time of a three-phase input, on the other hand, a relay 17 for three-phase/single- phase discrimination is turned ON, a constant-current control is executed by a prescribed reference signal of a DC set voltage and thus the improvement of an input power factor and reduction of higher harmonics of the input current are attained.