PURPOSE: To make the most of holding capacity of a servo motor by providing a control means for computing the effective current value from the current value of the servo motor detected by a detecting circuit and an action cycle of a robot and comparing the effective current value with the reference value to increase/decrease the acting speed of the robot.

CONSTITUTION: Electricity of a servo motor 3 during the action of a robot is detected by a detecting circuit 4, converted into a digital signal by an analog- to-digital converter 5 and sent to a main CPU 1. In the CPU 1, an action cycle is calculated from an internal timer, and this current value is recomputed into the effective current value by an arithmetic means 6. The computed effective current value is compared with the reference value stored in a memory, by a comparing means 7. In the case of the computed effective current value being smaller than the reference value, a servo driver 2 increases the acting speed command of the robot at a fixed rate, and in the case of the computed effective current value being larger than the reference value, the servo driver 2 decreases the acting speed command at a fixed rate. The action speed of the robot is increased/decreased by the servo driver 2 to the full holding capacity of a servo motor.