Forces applied to cause flection and extension movements of a joint of a subject (1) are detected by at least one force sensor (20a and 20b), and a joint torque for flexing and extending the joint is calculated based ON the forces. Further and a joint angle of the joint of the subject is measured by a sensor (30). Then, a change with passage of time in each of the joint torque and the joint angle during flection and extension movements of the joint of the subject is separated into a maximal extension position static phase, a dynamic flection phase, a maximal flection position static phase and a dynamic extension phase and a muscle tonus feature amount is extracted from a relationship between the joint angle and the joint torque in at least one of the dynamic flection phase and the dynamic extension phase. By using this muscle tonus feature amount and muscle tonus can be objectively evaluated with a method close to the medical examination manipulation that is conventionally performed by neurologists in medical examinations with an extremely simple apparatus.
