PROBLEM TO BE SOLVED: To excellently perform, with small invasion and along a preoperative plan, operations such as excision of the caput femoris, digging of the medullary space, and an installation of the femoral stem even in the case that the expansion of a surgical site is limited.SOLUTION: A stem installation instrument 10 is pushed by an operator so as to stride over an intertrochanteric crest 106 of a femoral neck 101, and is tightly fastened to a bone surface. A caput femoris 110 is cut along an edge AF of a contact fixation part (A) of the stem installation instrument 10. The medullary space of a femur 100 is dug from an insertion center point DX in a bone cut surface along a varus/valgus direction DA, an anteversion/retroversion direction DC, and a bending/extension direction DC. The femoral stem of a size determined in a preoperative plan is inserted into the medullary space of the femur 100 from the bone cut surface, and at this time, the insertion position DX in the bone cut surface, the varus/valgus direction DA, the anteversion/retroversion direction DB, and the bending/extension direction DC are referred, and the femoral stem is installed therealong.