To provide a machining method and device capable of reducing the manufacturing cost of a work.

Use condition of a tool, and a limit for determining the propriety of use of the tool from the use history of the tool to be used for machining are previously determined, and machining is performed according to the use conditions, where tools of which use history has reached the limit are replaced. The progress till reaching the limit is divided into a plurality of ranges and the use conditions are determined for every divided range. Machining is performed with changing the use conditions of the tool every time the use history of the tool exceeds the range and when the use level of the tool reaches the limit, the tool is replaced to another tool of the same kind.