Abstract—A driver operates the accelerattion pedal by perceiving reaction force in driving a car. In pedal design, it is necessary to design a reaction force characteristic that can improve the pedal operation feeling and the car acceleration feeling. In order to investigate the reaction force characteristic of the acceleration pedal, an ankle power-assist system which is able to assist the pedal operation of the car driver based on electromyographic (EMG) signals is developed. The effectiveness of the proposed power-assist system was evaluated under three kinds of driving postures.