PURPOSE: To shorten the forming time of a product by automatically recognizing a work remaining part to a blank and automatically and accurately forming a tool route for the work remaining part.

CONSTITUTION: A final tool route Ra1 for generating the product 12 by end mills 4a and 4b which are set based on the form of the product 12, the form of the blank 11 for generating the product 12 and a work condition including the radius r1 of the end mill 4a cutting/working the blank 11. An offset route ROFF1 obtained by offsetting the final tool route Ra1 by the radius r1 of the end mill 4a in a normal direction toward the side of the product 12 is generated, and a difference between the offset route ROFF1 and the form of the product 12 is obtained. The work remaining part K by the end mill 4a is generated based on the difference, and new tool routes Rb1-Rbn for cutting/working the work remaining part K by the new end mill 4b whose radius is smaller tan that of the end mill 4a are generated based on the work remaining part K.