PURPOSE: To obtain a torque controller by an economical voltage type inverter by dividing DC currents flowing through the inverter from a DC power by a voltage reference, obtaining motor currents and controlling the motor currents.

CONSTITUTION: An inverter 29 applies the AC voltage VM of a sine wave corresponding to a voltage reference VM' to a motor 18A by PWM control. When effective currents flowing through the motor 18A are represented by IM and a power factor by cos at that time, formula I holds from the relationship of energy balance. It is assumed that the operation power factor cos of the motor 18A is kept constant, formula II holds. Since output voltage VM is proportional to the voltage reference VM' and the power factor cos is held approximately constant within a working range, an output from a coefficient multiplier 33 takes a value proportional to the currents IM of the motor 18A. Accordingly, the currents IM of the motor 18A are controlled to the value of a current reference IM', thus controlling torque.