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 at the first stage of initial period of bend of knee joint, T1, is made small, while the second torque at the second stage of final periodof further advanced bend of knee joint, T2, is made large. As different from conventional ones, T1≤T2, and the load on the hip joint muscle of prosthetic limb user can be reduced.