When the torque command value (Tr*) is zero, a set point (Idc*) of DC current for an inverter (8) is calculated to obtain a difference between the set point (Idc*) and a detected DC current (Idc) so that an error (”¸e) in magnetic pole position may be estimated and corrected. By correcting the magnetic pole position, unwanted power running and regenerative torque of the motor can be avoided and unnecessary charge or discharge to or from a battery (9) can be prevented.