PURPOSE: To enhance the safety of a robot for polishing, by generating a slip in a reduction means built in the root end part of an arm and stopping or pressing the arm to be returned when large external force in a predetermined value or more is applied to the arm.

CONSTITUTION: Arms 8, 13 are driven by servomotors 25, 40 as power supply and by transmission torque of a reduction machine built in a root end part of the arm 8. The transmission torque of the reduction machine, being limited by a value of brake torque given to brake discs 23, 41 integrally formed with a casing 5, is obtained by friction force generated between the discs 23, 41 and brake members 50, 50, 51, 51, causing a slip to be generated between discs 23, 41 and the brake members 50, 51 ans stopping or pressing the arms 8, 13 to be returned when external force in a predetermined value or more is applied to the arms 8, 13. The transmission torque is limited by adjusting a spring 55 and a brake friction coefficient.