PURPOSE: To perform truth/flase judgment of rotational direction accurately by providing means for continuously monitoring a signal delivered from a rotational direction sensor associated with a step motor thus monitoring the rotational direction of the step motor and means for conducting truth/flase judgment of the rotational direction of the step motor based on the results of monitoring.

CONSTITUTION: A step motor control system comprises a step motor 101, a direction sensor 102, a direction monitoring section 103, a truth/flase judging section 104, and a control section 105. When the step motor 101 is rotated forward or reversely through the control section 105, the direction monitoring section 103 constantly monitors signals delivered from the direction sensor 102 and notifies the result to the truth/flase judging section 104. The truth/flase judging section 104 conducts truth/flase judgment of the rotational direction of the step motor based on information fed from the control section 105 and the result of monitoring delivered from the direction monitoring section 103 and notifies flase result to the control section 105.