In a motor feedback control, the current supply phase is set on the basis of the encoder count of an encoder and the current supply phase is also set on the basis of the encoder count by time-synchronous processing. In the feedback control, a maximum value or a minimum value of encoder counts is stored with updating. The rotation reversing is determined by comparing the present encoder count with the maximum value or the minimum value. If reversing is detected, the reverse rotation is stopped by fixing the current supply phase. If a disconnection is detected in windings of one phase in starting a motor feedback control, one of the other two phases for which no disconnection is detected is set to the first current supply phase.