PURPOSE:To alleviate a torque ripple generated in a permanent magnet rotor by flowing a drive current of 90 deg. flowing angle of an electric angle and a drive current of 180 deg. flowing angle of an electric angle to a stator winding. CONSTITUTION:Drive currents i1', i2', i3', i4' of 180 deg. flowing angles of electric angle formed of pretransistors Q12, Q13, Q14, Q15 and control transistors Q2, Q3 are respectively flowed to stator windings I , II, III and IV. Drive currents i1'', i2'', i3'', i4'' of 90 deg. flowing angle of electric angle formed of pretransistors Q8, Q9, Q10, Q11 and control transistor Q1 are flowed to stator windings I , II, IIIand IV. Since the torque ripples generated at a permanent magnet by these drive currents cancel from each other, the ripples are reduced.