In this paper, the method which eliminates the reactive operational force in bilateral control system under time delay is proposed. In bilateral control system under time delay, an operator feels large operational force. In addition to that, amplitude of response increases and it makes system unstable. In this paper, the proposed method eliminates this increasing. Therefore, operationality in free motion is improved. To solve this problem, reactive operational force is introduced which is calculated by using power factor in mechanical system. Power factor in mechanical system is derived from power factor in electrical system. Then, the concept of power factor is explained. In this research, only free motion is considered. Then, contact motion should be considered in future work. The performances of the previous method and the proposed method are evaluated through experiments.