This paper describes the formulation of the torque and angular velocity that can be output by the regenerative servo clutches, which was developed by authors previously for the concept of “Human-Powered Robotics”. The formulation has been done in consideration of the characteristics of the regenerative brake, differential gear mechanism, electric circuit and operator’s biomechanics. The optimization example for having maximum area of the formulated operation range is also introduced. The reasonability of the formulated operation range is confirmed by comparing with experimental results.