To prevent halfway fracture deviated from a cutting direction caused by losing internal stress balance in machine cutting.

This machine cut manufacturing method is to cut ring members 1 hardened by thermal processing into two semicircular members 1a by machining. The heat conduction and the thermal stress of a model of the ring member 1 are analyzed so as to find a stress expansion coefficient KI of the cut surface tip of the ring member 1. The cutting is performed while controlling that the found stress expansion coefficient KI of the cut surface tip does not exceed fracture toughness values KIC of respective parts of the ring member 1. The contents of controlling not to exceed the values are, for example, to set the cutting direction P and the cutting depth H.