PURPOSE: To control the original point position of a mobile part accompanying an original point return action without using any sensor for a device which performs the addition/subtruction of the number of pulses of the pulse signals outputted from an encoder by a counter and controls the movement of the mobile part based on the count value of the counter.

CONSTITUTION: A mobile part is moved toward a reference position (steps S1 and S2). When the count value of a counter has no change for a fixed time (YES in S4), the count value of the counter is compared with its initial value that is set when the mobile part is moved to a prescribed reference position (S6). Then, the count value of the counter is corrected into its initial value only when the difference between the count value of the counter and its initial value is kept in an allowable range (S7).