In the present day, there is demand for making robot being assistant in many kinds of cooperative tasks with human being, for example, in the medical service and welfare work. Such robot is supposed to be without sense of incongruity felt against human being and with the ability of executing smooth movement in human-robot cooperative task. In view of every motion of the human body being in naturally perfect smoothness, it is essential to analyze the human motional characteristics by introducing human model for establishing the law of control on the cooperative robot with human being. In this study, master-slave cooperation more appropriate for human-robot cooperative task was adopted. The experiment was carried out founded on the hypothesis that the human arm around the elbow joint was considered as a simple mass-spring-damper dynamic system with one end fixed. Upon main investigation into the slave's relaxed arm in clockwise motion, by virtue of examining the physical parameters in the mathematical model of the human arm, its impedance characteristics were recognized. It was found that as for human ordinary motion, the damping factor was low enough to be disregarded and the stiffness possessed individually linear property. And besides, the friction-like force was discovered to exist.