In the present invention, the velocity of a motor is controlled by fuzzy inferential reasoning in a transitional period when the motor is started, changed in speed, reversed or stopped. Such fuzzy control eliminates an increase in the length of transitional period caused by a limitation in supply current under conventional PLL control and makes possible a rapid transition to a target velocity. A plurality of fuzzy rules (1030a) are provided and one of these fuzzy rules (1030a) is selected in accordance with the length of the previous transitional period, thereby suppressing the effects of load fluctuation and the influence of a fluctuation in torque caused by a rise in temperature. Therefore, the length for transitional control of a motor can be shortened and the apparatus is reduced in size.