The disclosure relates to a technology of a manual lock mechanism for manually switching over the oscillating motion of an upper member and a lower member at a knee joint between a locked condition and an unlocked condition. More particularly, the disclosure aims at a simple structure of the manual lock mechanism and a size reduction of the knee joint or an artificial leg including the manual lock mechanism. For these purposes, one of oscillating shafts for swingingly coupling the upper and lower members is regulated. Therefore, the manual lock mechanism includes an oscillating shaft including an irregular part and a lock member for regulating the movement of the oscillating shaft. The lock member can be switched over between a locked condition where the lock member is in contact with the irregular part of the oscillating shaft and the unlocked condition where it is separate from the irregular part. When the lock member is in the locked condition, force from the oscillating shaft is applied as compression load in the longitudinal direction of the lock member.
