There are provided a sensor (113) for sensing the velocity of an AC motor (101), a sensor (112) for sensing an actual current flowing into the AC motor (101), a power drive circuit for driving the AC motor (101), and a control unit (108) for performing a velocity loop computation to obtain a current command from an offset velocity between a velocity command for the AC motor (101) and the sensed actual velocity, and for performing a current loop computation to obtain an offset current between the current command and the sensed actual current. In the current loop computation performed by the control unit (108), there is obtained a velocity compensation signal by amplifying the sensed actual velocity by a predetermined magnification, the command for the power drive circuit is compensated by the velocity compensation signal, the current loop computation is executed at a sampling period shorter than that at which the velocity loop computation is executed, and, at the time of the velocity loop computation, the actual current at the relevant sampling instant is estimated from the current command value of the previous sampling, and a current command is computed from the estimated actual current and the offset current.