PURPOSE: To set DC voltage to be lower and lower the voltage resistance of component parts used for a main circuit, by controlling the phase of input current according to the degree of the input current so that input voltage may be almost constant.

CONSTITUTION: The DC side voltage of a converter 3 is detected by a DC voltage detector 6. The voltage of an AC power source 1 is detected by an AC voltage detector 24, and the phase angle of the AC power source 1 is detected by a power phase detecting circuit 25. The input of the detection signal of a detection circuit to a micro-computer 26 is provided, and from the output of a DC voltage detector and a constant value corresponding to the voltage of the AC power source, the phase angles of AC line voltage for the input voltage of the converter 3 set to be almost constant, and the input current of the converter are computed, and from the phase angles and the output of the phase detecting circuit 25, the current command signal of the converter 3 is computed.