PURPOSE: To perform copying of a model in a complicated stereo shape the copying width of which is also set on a surface paralleling an axis Z by a method wherein a copying surface for an exclusive use is produced along a base lone three- dimensionally set at each copying bus, and only a portion within the given region thereof is copied.

CONSTITUTION: A copying surface 11 vertical to a line 3a formed such that a base line 3 set by interconnecting inputted coordinate values through a straight line is projected on a plane X-Y is created in a position containing a copying starting point Ps. A circular region 11a with a radius R is decided on the plane 11 centering around an intersection point Pc1 between the plane 11 and the line 3. Copying is performed such that a stylus is moved from the point Ps in a specified copying direction at a given speed, and is elevated in the direction of an axis Z along the shape of a model 1. Pick feed with a given width is effected from a point, where the stylus is moved to the boundary of the region 11a, in parallel to the line 3 and in a direction from point P1 to P20 or in a reverse direction. A feed completion point forms a copy ing starting point, a difference copying plane is created in a position vertical to the line 3a containing the starting point, and copying is effected on a copying plane in a reverse direction to that of preceding copying.