Abstract: An artificial cement-less hip prosthesis stem comprises an inner construct 7 which reacts with a load acting on a hip joint and an outer construct 8 for transmitting the load acting on the inner construct to a femur 1. The inner construct has an inner body 7B which reacts with the load transmitted from a neck 7A. The outer construct has both an outer body 8A which is bell mouth-shaped toward an epiphysis so as to surround the inner body 7B and a leg 8B extending toward a medullary cavity. The torsional rigidity given to the proximal end and the distal end of the outer body 8A and the leg 8B is regulated so as to be lower than the torsional rigidity given to an intermediate portion 18 of the outer body 8A.