PURPOSE: To control a motor in a closed loop without using an encoder by comparing the frequency of a drive pulse detected by drive pulse detecting means for detecting the drive pulse to be supplied to a coil of a stepping motor with that of a reference pulse, and correcting the drive pulse in response to the frequency difference.

CONSTITUTION: An analog-to-digital converter 6 detects an A-phase voltage at a predetermined threshold level to convert it into a pulse signal, and inputs it to a CPU of a microcomputer 1. The CPU applies a signal corresponding to a stored peak current value of a resistor 8 at the time of a predetermined rotating speed to a reference voltage circuit 2, which converts it to an analog signal, which is input to a comparator 3. The output decides the duty ratio of the drive pulse. A chopper 4 generates a pulse at a predetermined duty ratio in a predetermined frequency, and controls its rotating speed through a transistor 7. On the other hand, the output of a pulse generator 5 is applied to the base of a motor control transistor to control a rotating phase.