PURPOSE:To improve reliability, by mounting a circuit for detecting false operation by comparing and operating the number of pulses input to an exciting phase counter and exciting phases before starting the revolution of a motor of said counter and after stopping the revolution. CONSTITUTION:Contents that an exciting phase counter 1 must have after suspending the revolution of a step motor are computed by means of a computing circuit 14 from the contents of the exciting phase counter 1 before starting the operation of the step motor and the quantity of a moving quantity set device 10, which sets, that is, the number of pulses input to the exciting phase counter 1, and the computed results and the contents of the exciting phase counter 1 are compared by means of a coincidence circuit 15. When no coincidence between both the results and the contents of the counter 1 is decided by means of the coincidence circuit 15 when stopping the revolution of the step motor, the output ''1'' of the coincidence circuit 15 is set to a flip-flop circuit 16 by signals showing the suspension of the rotation of the step motor from a differentiation cricuit 13. Thus, an abnormality annunciator 17 emits signals indicating the false operation of the exciting phase counter 1 to the outside.
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