This paper deals with an above-knee prosthesis (AKP) that allows stair ascending/descending with no external energy source. It controls the passive resistance and interlocking strength of the knee and ankle joints with a flow control valve (FCV) equipped with a hydraulic system. The FCV is also mechanically controlled by an automatic flow controller (AFC). Our previous study certified that the experimental AKP allows step-over-step gait in stair ascending and a slight knee flexion at the initial stage of the stance phase in level ground walking, as observed from non-amputees’ walking. However, the experiments showed that the AKP does not allow smooth flexing of the knee in the stance phase during stairs descending because of the improper timing of the AFC opening. This paper shows the total walking performance of the AKP equipped with a refined AFC.