A control device for controlling a three phase AC motor with an inverter includes: a sensor phase current acquisition device for a sensor phase current sensed value; a rotation angle acquisition device for a rotation angle sensed value; a number-of-revolutions operation device for the revolution number; a current estimation device for a current estimated value; a first voltage command value operation device for a first voltage command value; a voltage command reference value operation device for a voltage command reference value; a second voltage command value operation device for a second voltage command value; a control mode switching device for switching to a first control mode when the revolution number is more than a threshold, and switching to a second control mode when the revolution number is not more than the threshold; and a torque abnormality monitoring device for monitoring an output torque during the second control mode.