In a surgical operation for replacing artificial knee joints, before a regular (genuine) implant is mounted as a femur-side member, a resection is performed along a pre-cut line shallower than a genuine-cut line, and a pre-cut trial is mounted； and the extended position and the flexed position and the rotation during flexion are observed, so that it is judged whether the set-up genuine-cut and implant are appropriate. A pre-cut trial is mounted on a pre-cut line which is cut shallower than a genuine-cut line, and the extended and flexed positions of a femur and the state of flexion thereof are observed so as to make judgment whether the genuine implant is appropriate, the pre-cut trial being modeled after the genuine implant which is mounted on resected surfaces formed by genuine-cut performed so as to form the end resected surface, posterior and anterior resected surfaces, and the posterior and anterior chamfer-resected surfaces on the distal end of the femur.
