Robots are taken attention as one of key solutions for nursing care field along with aging of population. In the nursing care field, the robots have to work in the limited space and contact with humans directly. Therefore miniaturization and precise force control are two important issues for nursing care robots. Then a tendon-driven rotary actuator with thrust wires and a polyethylene (PE) line was developed, and wire tension control system has been researched to solve the two important issues in our previous study. However, the rotary actuator did not show good force control performance due to the mechanical force loss in the thrust wires. In this paper, a force loss rate is identified, and compensation method for the tendon-driven rotary actuator is proposed with wire tension control in order to achieve precise force control. Compensation experiments are implemented to confirm the validity of the proposed method.