The present invention provides a knee joint that is capable of widening a moveable range, and that has good energy efficiency and is small and light weight. The present invention also provides a knee joint that is of an active type, but comparatively inexpensive. A drive section 1 moves a driven member 21. An elastic member 22 is arranged between a driven member 21 and a linear motion member 23. The linear motion member 23 elastically moves in at least one direction, in accordance with movement of the driven member 21, by means of the elastic member 22. A crank mechanism 3 can realize bending and extension of the knee joint by converting linear motion of the linear motion member 23 to rotational motion.
