There is prepared V-CAD data obtained by dividing external data 12 consisting of boundary data of an object into rectangular parallelepiped cells 13 having boundary planes orthogonal to each other in accordance with octree division and separating the respective divided cells into internal cells 13a positioned on the inner side of the object and boundary cells 13b including a boundary face, and mold data and mold processing data used to manufacture the object are generated from data of a reference plane which at least partially comes into contact with the object 1 and the V-CAD data. Further, in the mold processing data, a plurality of the processing tools 2 are selected in descending order of a size in accordance with sizes of the internal cells 13a of a processing portion, and the processing tool 2 is moved in a plane of the mold and in the thickness direction, thereby processing the mold. As a result, by using the V-CAD data, the NC processing program for mold processing can be simplified, and the mold processing time can be greatly reduced.