PURPOSE: To improve the effect of damping and carry out more stable power control by providing a means (memory) for processing a signal at a longer sampling time than the signal sampling time of a digital converting means in a transmission system from the digital converting means to a comparing means via a proportional control means.

CONSTITUTION: When a joint torque which is an external signal is obtained by a torque detector 2, this signal is digitally converted for each sampling time by means of an A/D converter 6 and stored in a buffer memory 11. Then, a target torque and the joint torque which is outputted from this memory 11 for each time are inputted into a proportional adjusting portion 10 where a driving torque value necessary for generating the target torque in an arm mechanism 1 is calculated, and stored in a separate memory 12. On the other hand, the joint torque is differentiated in time by a differentiating portion 9 and then, multiplied by a constant in a multiplying portion 8 and this value and a value outputted from the memory 12 for each time are read into a comparing portion 7 and the output value thereof is converted into analog by a D/A converter 5 to drive an arm mechanism 1.