PURPOSE: To reduce the speed variation of a brushless motor by driving the motor with an output chopped from an output from a coil conduction logic circuit when the period of speed discrimination is long.

CONSTITUTION: If a discrimination period for discriminating the slow or fast of the rotating angle speed of a rotor shaft to a target angle speed is one conduction logic period or more output from a coil conduction logic circuit 1, a brushless motor is driven by an output chopped from the output from the coil conduction logic circuit 1. As a result, the amplitude of a speed hunting is reduced as compared with the case where a DC brushless motor is driven with an output responsive to the slow or fast of a discrimination speed for discriminating the slow or fast of a rotor shaft rotating angle speed to a target angle speed. Thus, speed variation can be reduced.