We have aimed at the development of the robot arm that operates safely on the site of nursing and welfare. Therefore, we develop the robot arm that is used a pneumatic artificial muscle as the actuator. Before time, the robot arm with antagonism structure that is used a pneumatic artificial muscle unit as the actuator is developed. But the angle of the joint can't be filled enough with such a robot arm. Then, we proposed the system that improved amount of shrinkage and contractile force, and the robot arm that had the joint drive angle equal with human was developed. Result of experiment of arm drive, the joint drive angle equal with human is achieved, and the effectiveness of the mechanism was confirmed.