PURPOSE: To avoid a crash between a slave arm and mechanical stopper in an operational limit and prevent occurrence of damage of the slave arm by gradually reducing a servo-gain as the slave arm approaches the operational limit.

CONSTITUTION: The captioned master/slave manipulator operates joints of a slave arm so that a deviation between joints angle of a master arm and that of slave arm is made to be zero. The above manipulator is operated to gradually reduce a servo-gain GS as the deviation PH (=PL-PS) is reduced, wherein PL, PS are the limited position and the present position in an operational angle of the slave arm respectively. This causes the slave arm to be sequentially reduced in the operational speed so as to prevent a rapid action in the vicinity of the operational limit thereby it is possible to avoid a crash between a mechanical stopper and a slave arm so as to prevent occurrence of damage of the mechanical stopper and a slave arm.