To facilitate the high speed and smooth driving of an electric motor and facilitate the reduction of noises of the motor by a method wherein the revolution of the motor is compared with a threshold value and a first state in which the revolution is smaller than the threshold value and a second state in which the revolution is larger than the threshold value are discriminated from each other and the control operation of a negative feedback control means is switched in accordance with the discrimination result.

A first state in which the revolution of an electric motor is smaller than a predetermined threshold value and a second state in which the revolution is larger than the threshold value are discriminated from each other by a negative feedback control switching means. If the revolution of the motor is not smaller than 500rpm or, if the revolution of the motor exceeds 300rpm and a high speed flag is set, the feedback control is not performed. If the revolution of the motor is not larger than 300rpm or, if the revolution of the motor is smaller than 500rpm and the high speed flag is cleared away, the feedback control is performed. As a result, in the high revolution state, the number of processes to be performed for the negative feedback control can be reduced and, further, in the low revolution state, the high precision negative feedback control can be performed, so that, the smooth rotation driving in the high speed state and the noise suppression in the low revolution state can be realized.