To realize highly reliable motor drive by performing such a drive control as causing no stop of a motor upon occurrence of a disturbance during 180° conduction drive.

During 180° conduction drive, a motor current detecting means 11 detects a motor current. Upon occurrence of an abnormality in the motor current, a disturbance monitor section 6 makes a decision that a disturbance has occurred. A drive system selecting section 7 then makes a switch from 180° conduction drive to intermittent conduction drive.