PURPOSE: To automatically calculate a cutter path when a shape is corrected by a CAD/CAM system.

CONSTITUTION: When the shape after the calculation of the cutter path and the generation of NC data is corrected by CAD by utilizing the customizing function 4 of the CAD system 1, a cutter path calculating process and an NC data generating process are automatically called (A1). In response to the calling, CAM 2 calculates the cutter path and generates NC data for the corrected shape according to a cutter path calculation result list containing machining condition data set for the shape before the correction (B7-B11). Even when the shape is corrected, the shape is hardly in discordant with the cutter path.