To provide an NC data generation system in which all works can be machined together successively in the order of used tools.

When a work name 'AA' is inputted, its tool trace file is read-in sequentially to read only the data indicating an operation order, etc., and tool data 1, 2... are entered into an array table 31 in use order. A stage 32-2 is additionally generated as a section area to be used for the process of a next stage and tool data are entered therein in the use order reverse to the use order of all tools set previously to a stage 32-1. For a work BB, tool data 1, 2... are similarly entered. Words CC and DD are the same. The tool data are related to machining coordinate position data of tools and tool trace file names. The tool data are read out of this array table 31 laterally from the top stage line to read corresponding tool trace files out, and they are connected to automatically generate machining order NC data 41 by the tools.