PURPOSE: To prevent the stop position from shifting due to step-out by conducting the positioning based on a set number of positioning steps.

CONSTITUTION: A setting means 18 sets a plurality of different third numbers of steps by adding second numbers of steps, obtained by subtracting 1 and 2 from the number of patterns of exciting phase, to a first number of steps while being designated by a designating means 12. After a detecting means 10 detects a movable part 80, the step motor is reciprocated in the direction of a stopper 84 and when the fourth number of steps, i.e., the number of steps in the return path, matches the third number of steps, the third number of steps is set as the number of positioning steps and stored in a memory means 20. When the positioning is conducted after releasing the designating means 12, the movable part 80 is shifted by the number of positioning steps being stored after it is detected by the detecting means 10 and then stopped by a stopper 84 to be positioned. This constitution prevents the stopping position of the movable part 80 from being shifted from the stopper 84.