— We have proposed the concept of Man-Machine Synergy Effectors. These are high-performance tools for human use, which are realized by introducing robot technology. It becomes possible to perform conventionally impossible tasks by human alone or robot alone, because the system synergizes better assets of both parties. In this paper, the concept of ManMachine Synergy Effector is described. Then, the Power Pedal is introduced as a prototype of Man-Machine Synergy Effector for human lower extremities, which amplifies human leg power intuitively.