PURPOSE: To control the armature current of a motor to flow depending on a command value by obtaining deviation from a current instructing value by detecting a value of combined current flowing through an inverter circuit and controlling the ON/OFF of an inverter circuit on the basis of such deviation and an output of commutation sensor.

CONSTITUTION: A value of an instruction Ir of the current to be made to flow into a 3-phase synchronous motor 8 of each constant period is received. Next, a combined current IS of an inverter circuit 7 to which a total sum of currents flowing into each phase is detected by a current detector 1, this value is digitized by an A/D converter 2 and then it is converted to a feedback current value If. Next, deviation Id between current instruction Ir to be made to flow into the motor armature and feedback current value If is obtained by an adder 3. Next, the compensating calculation such as PI control etc., is conducted with a compensating 4 to the deviation Id and the PWM width Cu, Cv, Cw, of each phase are obtained by the PWM circuit 6 from the result of calculation. Simultaneously, a switching pattern of the inverter circuit 7 is determined from the commutation signal CS detected by the commutation sensor 5.