PURPOSE: To prevent deviation of a track due to a load change, etc., by comparing a current command to a motor with a predetermined set current, reducing a target speed if the command is larger than the set current, and regulating the command to each motor to the set current or less.

CONSTITUTION: Current command comparators 28X, 28Y compare a current command to motors 10X, 10Y with a predetermined set current. As a result of comparison, if the command is larger than the set current, the command to the motors 10X, 10Y is regulated to the set current or less by a target speed regulator 30. Thus, even if tracking becomes difficult due to an overload, etc., the target speed is reduced. As a result, the tracking is secured, and a target locus can be drawn. Thus, a deviation of the locus due to the load change, etc., can be prevented.