The biarticular muscle that synchronizes the knee joint with the ankle joint plays an important role in the jumping motion. In order to reproduce the biarticular muscle, in the present article, we have developed a jumping robot with a variable geared mechanism using a planetary gear. When the planetary gear is not used, the ankle joint movement synchronizes with the movement of the knee joint. By using the planetary gear, that rate becomes variable. The robot with two-joint gear mechanism can drive the ankle joint without driving the knee joint. Therefore, the robot can determine the direction of the jump from the movement of the ankle joint. The robot mimics the human jumping motion, and it executes the jump experiment. Therefore, the developed robot was able to satisfactorily mimic human jumping action, and its motion was analyzed.