In research of biped walking robot, energy-efficiency is an important issue. Full-actuated type robots using ZMP based control have high environmental adjustability and high robustness, but they consume much energy. On the other hand, passive dynamic walking type robots have high energy-efficiency, but they don't have high-environmental adjustability and robustness. Then, we have proposed an optimal trajectory planning method to obtain the energy-efficient walking under full-actuated model. In this paper, we used the circular feet model in walking performance analysis, and showed the advantageous effect of circular feet. Finally, we evaluated the energy-efficiency of our robot and other types of robots by using specific cost, and showed the effectiveness of this method.