This paper is concerned with the human-robot system such as power assist system based on the position-controlbased impedance control (admittance control) . The system has two force inputs from the operator and the environment, which may cause the vibratory behavior when the robot comes in contact with the environment. It is because the operational force and the contact force do not balance due to the noise, error, delay and so on. This paper proposes the admittance control with two inputs that achieves steady contact with an environment by modifying the contact force information. The effectiveness of the proposed method is demonstrated through several experiments.