PURPOSE: To suppress ripple of output current from an inverter by arranging a DC/DC converter and a ripple detecting circuit on the input side and adding a detected value of AC voltage ripple, variable with same polarity as the increasing/decreasing direction of ripple, to an output frequency command value.

CONSTITUTION: A DC/DC converter 6 receives an output voltage Vdc from a DC intermediate circuit and produces a DC voltage Vro proportional to a constant DC voltage Vco and the voltage Vdc. AC ripple component in the voltage Vro is detected, as a voltage signal Vr having proper level, through a ripple detecting circuit 8. An output frequency command fs is obtained by adding an inverter output original frequency command fso and the voltage signal Vr in an adder 9. An AC motor 5 is subjected to rotation control with a rotation corresponding to the output frequency command fs. By such arrangement, ripple of output current from an inverter 4 can be suppressed.