Wearable robots, especially power suits to enhance human activity are one of the most interesting and important topics. This study aims t o develop a wearable robot that is small-size, light-weight for improving human perfor- mance and reducting muscle fatigue. So we proposed smart suit with variable stiffness mechanism that utilize
elastic forces for assist and make assistance control by impedance control. Because of to utilize elastic forces for assist, the capacity of the suit do not reliance on weight of actuators and their's energy source well than conventional power suits. In consequence, we think the suit can realize miniaturization and getting light-weight. In a previous study, we verified the effectiveness of smart suit with variable stiffness mechanism by experiments and simulations in order to design the suit which can tune the stiffness of joint mechanically, and had been able to confirm the effectiveness. Based on these results, we design the smart suit with variable stiffness mechanism that be able to control number of working spring by small actuator, and at any knee joint angle, elastic energy occurrence is variable by displacement angle of ankle joint. We could obtain a result of the output per a mass of the suit is more large than conventional power suits. And we confirm that reducting muscle fatigue by experiments on knee bends and walking in case that subjects wear the suit. In this paper, we show the suit that we developed and effectiveness of the suit for human working.