PURPOSE: To avoid occurrence of a damage of a mechanical stopper and a slave arm in an operational limit, in the case that a slave arm approaches the operational limit beyond a predetermined position in the vicinity of the operational limit, by adding, to a reduction force, a gradually increasing force as a slave arm approaches the operational limit.

CONSTITUTION: In a bilateral type master/slave manipulator control system, in which an external force Ts applied on a slave arm is operated for feed-back to a master arm, a predetermined position is set in the vicinity of an operational limit of a slave arm. In the case that the slave arm approaches in the vicinity of the operational limit beyond the predetermined position, the nearer it approaches, the more a force corresponding to a joint angle Ps is applied to a reaction force Tm. This make the master arm less liable to be driven, thereby suppressing operation of the slave arm. Thus, it is possible to relay any shock caused by abutment of the slave arm on a mechanical stopper so as to avoid a damage thereof.