Inverter device

This invention provides an inverter device that can detect a step-out state of an AC motor by a simple process without depending on a rotation speed of the AC motor and also surely hold an abnormal state in the step-out state of the AC motor. The inverter device 1 includes a torque current control unit 6 for controlling a torque current direction voltage so that a given torque current command value coincides with a torque current detection value, and a V/f conversion unit 7 for calculating an induced voltage command of the AC motor 2 based on a given output frequency command. The inverter device further includes a step-out detection unit 10 for detecting a step-out state of the AC motor 2 based on the torque current direction voltage and the induced voltage command.