Forces applied to cause flexion and extension movements of a joint of a subject (1) are detected by at least one force sensor (20a, 20b), and a joint torque for flexing and extending the joint is calculated based on the forces. Further, 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 flexion and extension movements of the joint of the subject is separated into a maximal extension position static phase, a dynamic flexion phase, a maximal flexion 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 flexion phase and the dynamic extension phase. By using this muscle tonus feature amount, 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.
