Analysis of human running has revealed that the motion of the human leg can be modeled by a compression spring because leg’s joints behave like a torsion spring. In addition, the pelvic movement in the frontal plane contributes to the increase in jumping force. We therefore assumed that human-like running, which requires higher output power than that of existing humanoid robots, could be realized based on these characteristics. Hence, we developed a model composed of a body mass, a pelvis and a rotational joint leg, and fabricated the leg by incorporating a stiffness adjustment mechanism that uses two leaf springs. In this way, we were able to achieve a human-like joint stiffness, which could be adjusted by varying the effective length of one of the leaf springs. We achieved hopping by resonance of the pelvic movement and joints’ elasticity.