To increase the machining efficiency by fast tool movement in a detailed shape machining.

After several guide dot sequences GL of tool paths for detailed part machining are generated according to contact point track dot sequences found by performing a rolling process wherein a sphere B having a radius equal to the radius of a large-diameter tool is rolled in contact with the wall surface WF and bottom surface BF of a product shape along the recessed ridge at the border between the wall surface WF and bottom surface BF, tool center position close inspection points PDP are set on the guide line dot sequences between the respective constituent points GCP of the guide line dot sequences GL and their constitution points GCP along the respective guide line dot sequences GL. Tool center positions TC are found as to those tool center position scrutiny. When a tool path for detailed shape machining by a small-diameter tool ST is generated by connecting those tool center positions TC, the nearest point NP is found from each tool center position close inspection point PDP in each guide line dot sequence GL on the center point dot track point sequence BCL of the sphere B at the time of a rolling process. The position of the center point of the tool tip part in a spherical shape, when the small-diameter tool ST moved from each nearest point NP to the corresponding tool center position scrutiny point PDP comes into contact with the wall surface WF or bottom surface BF, is regarded as a tool center position TC.