PURPOSE: To compensate for the counter electromotive force depending on the variation of electric angle and current by determining a compensation value based on the actual current value and/or the electric angle of a motor and the rotational speed thereof and compensating for a voltage command using the compensation value thus determined.

CONSTITUTION: A voltage command from a current loop gain block 3 is added with a counter electromotive force compensation value to produce a compensated voltage command for driving a PWM amplifier. A counter electromotive force compensation block 10 receives the rotational speed of rotor from a speed detection block 7, motor actual current i from a current detector block 8 and the electric angle θ of rotor from an electric angle detection block 9. The compensation block 10 determines a corresponding counter electromotive force compensation value Vc which is added to the voltage command before the counter electromotive force is compensated. Consequentiy, the counter electromotive force can be compensated for depending on the electric angle θ and the current (i).