To limits the current while taking account of overcurent protection at low frequency at the time of motor stall or the like by limiting the current command value below a predetermined current limit value depending on the frequency of AC current being fed to a motor.

A current limiter 50 reads out a current limit value I1lim from an angular speed-current limit value table in a memory 51 according to an angular speed corresponding to an AC voltage frequency ω1 being applied to a stator winding from an adder 26. A q-axis stator winding current limit value I1qlim for limiting the current command value Ilq* of q-axis stator winding current variable depending on the load is then calculated based on the current limit value I1lim and a d-axis stator winding current command value I1d* outputted from a speed controller 30. The current command value I1q* of q-axis stator winding current being inputted to an adder 24 is limited below the q-axis stator winding current limit value Ilqlim. Consequently, overcurrent protection at low frequency can be performed inexpensively without derating a power converter 1.