A technology for making the sensation at use of prosthetic limbs utilizing a hydraulic cylinder and a spring cylinder as comfortable as at use of those utilizing a pneumatic cylinder and further for improving walk following properties. In particular, the arrangement of drag generating means, such as a hydraulic cylinder and a spring cylinder, per se is specified. Accordingly, the resistance produced by the drag generating means in accordance with an increase of knee angle is increased. The first torque T1 at the first stage of initial period of bend of knee joint is made small, while the second torque T2 at the second stage of final period of the further advanced bend of knee joint is made large, thereby satisfying a relation of T1≦T2, as different from conventional ones.