PURPOSE: To make operation within a constant plane at the tip of a slave arm achievable even if the handle part of a master arm is not operated within the constant plane by making the slave arm follow in the wake of the three- dimensional operations of the master arm when a plane operating switch is turned to OFF but at the time of being turned to ON, making it operate only within the constant plane.

CONSTITUTION: When an on-off signal of a plane operating switch 60 is inputted into a computer 51, a signal for operating a slave arm 1 is operated and outputted on the basis of each signal of respective potentiometers PT1 to PT3, PT11 to PT13 and the on-off signal. Supposing the switch 60 is turned on, a tip of the slave arm 1 operates within a constant plane in keeping its height when the switch 60 is turned on intact in relation to operations in the three- dimensional space of a master arm 10. If the switch 60 is tuned on, it follows in the wake of the operation of the three-dimensional space of the master arm 10 as ordinal control, whereby the tip of the slave arm 1 operates within the three-dimensional space.