This paper proposes a human-robot cooperative control of exoskeleton robot assisting muscle strength of a human upper extremity when lifting or transporting heavy objects. When a human wears a robot, the motions of the human and robot generate interaction, which is called HRI (Human-Robot Interaction). To generate reference motion from the interaction force, a pHRI model was developed using virtual mechanical impedance, and an experimental method to determine the impedance parameters of the pHRI model was proposed. The controller was developed in such a way that the desired motion will be controlled using dynamic model-based compensation. To verify the proposed control method, it was applied to an exoskeleton robot with 6-DOF for both arms. Motion-following-performance experiment and muscle-strengthassisting- effect experiment were conducted using this robot. Experimental results, the wearer of the exoskeleton robot can handle a small force was the heavy object.