Recently, healthcare for elderly people is a big problem in certain countries. As the candidate to solve the problem, robots have been taking attention. The robots, which work in the nursing care field have to have multiple-degrees of freedom (DOF) to achieve variety of tasks. At the same time, the robots have to be small to work in limited space like human living environments. To achieve the goal, a new rotary actuator, which is small and output enough torque for operation is needed. Then a tendon-driven rotary actuator with polyethylene (PE) line was proposed in our previous study. However, the deflection of the PE line was occurred and the performance was deteriorated due to it during control. In this paper, new control systems for the tendon-driven rotary actuator with the PE line are proposed. The tension of the PE line is controlled in common mode and the rotation angle is controlled in differential mode with modal transformation. Moreover, the tension and the torque are also controlled with modal transformation. With the proposed control systems, the tension of the PE line is controlled in the intended value and the PE line is stretched tightly during the rotation angle control and the force control. The validity of the proposed tension control systems are evaluated through experiments.