Abstract—In a super-aged Japanese society, it is very important to take advantage of engineering support for elderly assist. In recent years, many assistive and rehabilitation devices using the pneumatic (McKibben) artificial actuators have been developed in such a public situation. In this study, development of a rehabilitation device driven by pneumatic actuator is aimed. Thus, the purpose of this paper is to develop the McKibben artificial actuator with the built-in outer diameter sensor for position control. However, it is difficult to measure the displacement (length) of McKibben artificial actuator which does not lost the flexibility. The developed sensor measures the constraint position (outer diameter) of the actuator by using the Hall-effect (magnetic) sensor. In addition, this paper proposes the sensor characteristics between the displacement and the sensor value. The position control scheme is designed by solving the mixed sensitivity problem (robust stability and nominal performance) for the PAM (Pneumatic Artificial Muscle) system. As a result, the effectiveness of the 2 DOF (position) control system using the outer diameter sensor is confirmed by experimental results.