A large joint output is required for the robot to perform dynamic motions. Most previous robots output power only with actuators, with a lot of energy. On the other hand, humans perform with high efficiency by storing and releasing energy by tendons. When trying to simulate it with robots, the actuator and elastic element are arranged in series. This mechanism becomes complicated, large and heavy. Therefore, we propose a novel joint mechanism reducing the size and weight by designing using a 5-bar linkage. To make it easy to use for the joint mechanism, we propose to combine the 5-bar linkage and the 4-bar linkage. We developed an ankle joint of the robot with this mechanism. While demonstrating the same performance as the previous mechanism, we succeeded in reducing the size by 20% and the weight by 0.7 kg.