A manufacturing method of a bone cutting assist device 1 includes generating a bone cutting assist device model M representing the bone cutting assist device 1 including a fitting surface 12 that fits a surface of a bone model BM, a cutting slit 13 that guides a cutting jig, a first guide hole 14 for inserting a first rod model LM 1, and second guide holes 15 for inserting second rod models LM2. The manufacturing method also includes outputting three-dimensional manufacturing data representing the generated bone cutting assist device model M, and manufacturing the bone cutting assist device 1 according to the outputted three-dimensional manufacturing data.
