PURPOSE: To obtain driving torque stabilized also for the fluctuation of AC input voltage, by varying the driving frequency of a stepping motor based on an AC input voltage value.

CONSTITUTION: By an AC input voltage value detecting circuit 4, the voltage value of an AC input source 1 is detected, and voltage detecting signal 5 is fed to a stepping motor control circuit 6. From the stepping motor control circuit 6, according to the voltage detecting signal 5, the driving frequency signal 7 of high frequency is fed to a stepping motor driving circuit 3 if the voltage of the AC input source 1 is high, and the signal 7 of low frequency is fed to the circuit 3 if the voltage of the AC input source 1 is low. By the stepping motor driving circuit 3, a stepping motor 8 is driven with driving frequency specified by the driving frequency signal 7.