A femur supporting device includes a femoral stem having a plurality of inclined passages. The femoral stem includes an inner side and an outer side. Each inclined passage includes an outlet in the inner side and an inlet in the outer side. Each inclined passage inclines upward from the inlet to the outlet. A plurality of supporting rods extends through the inclined passages. A first engaging end of each supporting rod extends out of the outlet of one of the inclined passages. A second engaging end of each supporting rod extends out of the inlet of one of the inclined passages. The first engaging end of each supporting rod is engaged with one of a plurality of first engaging portions in a trochanter head. The second engaging end of each supporting rod is engaged with one of a plurality of second engaging portions of a fixing unit.