PURPOSE: To provide the damping method of a servo control system capable of damping the system without providing a mechanical detector for detecting the acceleration of an arm on the side of the arm.

CONSTITUTION: In the servo control system 10, the rotational angular velocity θm' of the driving shaft of a motor 3 is detected by an originally provided velocity detector 6. In the meantime, the rotational angular acceleration θa"Λ of the arm 1 is estimated from the rotational angular acceleration θm" obtained by a differentiator 9 based on the rotxational angular velocity θm' by an acceleration estimation device 7. The rotational angular acceleration θa"Λ of the arm 1 is fed back to the control command amount side of the motor 3, phase inversion is performed and the system is clamped. Thus, the need of providing the mechanical detector for detecting the rotational angular acceleration of the arm 1 is eliminated and the constitution of the arm 1 is simplified.