An angle detector 25 sets a q-axis command current to a first magnetic pole detecting current Iq_p1 and a second magnetic pole detecting current Iq13p2, and performs a magnetic pole detecting process to calculate a first magnetic pole reference value A1 and a second magnetic pole reference value A2 (t2-t3, t4 -t5), and detect the orientation of the magnetic poles of a rotor 2 of a motor 1 based on the sign of the difference &Dgr;A (=A1-A2) between the first magnetic pole reference value Al and the second magnetic pole reference value A2. The angle detector 25 effects a proportional process only on the difference between the q-axis command current and a detected q-axis current and the difference between a d-axis command current and a detected d-axis current to calculate a current difference (t2-t5) under current feedback control when the magnetic pole detecting process is carried out, and effects a proportional plus integral process on the above differences to calculate a current difference (t0-t2, t5-) under current feedback control when the magnetic pole detecting process is not carried out.