PROBLEM TO BE SOLVED: To provide an osteotomy pretreatment tool which enables a surgeon to confirm the amount of respective bones to be cut quickly, accurately, and easily before the osteotomy for forming the front side surface and the rear side surface at the distal end of a femur during surgery of artificial knee joint replacement, and facilitates osteotomy afterward.SOLUTION: The osteotomy pretreatment tool 1 is used before performing the osteotomy for forming the front bone cutting surface Ab and the rear bone cutting surface Ac of the distal end A2 of the femur for replacing a knee joint K with an artificial knee joint T. The osteotomy pretreatment tool 1 includes at least a gap block 10. The gap block 10 is placed on a proximal end surface Ba of a tibia cut perpendicularly to the functional axis Wb of a tibia B and abuts on the back A33 of the medial condyle and the back A43 of the lateral condyle of the femur A in a flexed position. Then, the gap block 10 keeps a posterior condyle axis Lx passing through the back A33 of the medial condyle and the back A43 of the lateral condyle of the femur A in the flexed position in a state to internally rotate with respect to the proximal end surface Ba of the tibia.
