PURPOSE: To attempt the automatic creation of NC program by providing a device computing a working range based on data for a work start point, a self-cut diameter, and a length, a CL data preparation device, and a device which performs the conversion into an NC format followed by transfer.

CONSTITUTION: Data inputs consisting of data for work start points SX and SZ when a tool is actually moved to the work start points, working diameters D1 and D2, the length JL of a pawl, and the length L of raw materials. Then these data are inputted into a working data preparation device 2 for preparing data based on SX, SZ, D1, D2, JL and L applicable to a raw pawl (a) for a part and a row pawl (b) for a rework. Subsequently, tool locus data are prepared by a CL data preparation device 3. And then said data are transformed into an NC format by an NC data conversion/transfer device 4 for sending them to a memory 5 at the NC side. As the aforementioned method is not for the input of a form working, an NC program is automatically created.