To switch a gain corresponding to the state of a load applied to a shaft to operate a robot at high speed within the range not to saturate an output torque.

This method has a step for finding the required acceleration/ deceleration time in the case of executing a moving command from the set acceleration/deceleration, step (S4) for proximately estimating the output torque of each axis motor at the time of acceleration and deceleration completion concerning the operating command generated based on this required acceleration/deceleration time and defining that value as an estimate torque and step for comparing (S5) this estimate torque with the previously stored torque parameter for comparison of each axis, setting low (S6) the gain of feed forward control when the estimate torque exceeds the torque parameter for comparison, setting high (S7) the gain of feed forward control when the estimate torque does not exceed the torque parameter for comparison and applying a command to the motor.