A three-channel bilateral control system which is hybrid of position control and force control in the acceleration dimension based on disturbance observer gets unstable in contact with environments under time delay. In this control system, the sum of master force and slave force is controlled to zero in common modal space to realize the law of action-reaction. This paper proposes a velocity damping method which suppresses the higher frequency vibration than the frequency of human motion. This method improves the stability of force control in the common modal space, maintaining good operationality. The validity of the proposed control system is confirmed by some experimental results.