PROBLEM TO BE SOLVED: To provide a knee joint appropriate for allowing a components of tibia and thighbone to rotate and swing at a very large bending angle.SOLUTION: A thighbone component includes a lateral condyle and a medial condyle extending to a front part to the rear part of the thighbone component. A thighbone gap is provided between the lateral condyle and the medial condyle, to extend to the front part from the rear part of the thighbone component. The lateral condyle and the medial condyle are jointed together at the front part of the thighbone component, to be positioned at a front end of the gap, for forming a patella tracking route or a support surface which form the front end of the gap. Both rear ends of the lateral condyle and the medial condyle are bridged, and a thighbone cam forming the rear end of the gap is provided. The thighbone cam is constructed so as to have a shape of one section of a ring 20. A tibia component is provided with two joint support surfaces being almost symmetrical on both sides of a central post. The joint support surface receives the lateral condyle and the medial condyle of the thighbone component, and the post is shaped so as to be inserted in the thighbone gap.
