We have developed a new long leg brace fitted with a computer-controlled knee joint that allows the user to go up and down a slope and stairs. Using this new brace, we analyzed gait under various conditions in ten normal men in terms of dynamic electromyography. Walking up a slope with normal step produced discharges in the leg muscles other than the gastrocnemius lateral head before and after the heel-strike on the ground, which indicated the absorption of the impact of landing. Going down a slope with controlled step resulted in lower activities of the tibialis anterior and the gastrocnemius lateral head than doing so with non-locked step or locked step. In subjects walking up stairs with tandem gait, the large discharges of the gastrocnemius lateral head that were observed in the late stance phase with normal step disappeared when the brace was applied. These results indicated that the muscle activity levels decreased during controlled walking with this new brace, and that the new brace can compensate for reduced muscle strength of the lower leg during walking. Kinematic analysis of walking revealed no significant difference between normal walking and controlled walking under any walking conditions.