Master-slave system with bilateral control is expected to be a key technology for the next generation robots. Since position and force information are transmitted bilaterally, operators can operate the slave robot in a remote place, and feel a tactile sensation of the remote environment. Thus, by utilizing bilateral control, teleoperation with high operationality can be realized. On the other hand, it can be said that the accuracy of the task depends on operator skill, and the burden of the operator is quite high. The purpose of this research is to realize a system which human can modify the task conducted by the slave robot autonomously. With such system, high efficiency of the robot and human skill can be integrated, and thus the burden of the operator will be reduced. In the proposed system, when the operator doesn't operate the master robot, the slave robot conducts the task according to the position command or the force command given beforehand. If the operator operates the master robot, these commands are modified according to human operation. In this paper, 4ch based virtual impedance controller is proposed to realize a desired system. Experiment is conducted to verify the validity of the proposed method.