When an item (T.sub.1 or T.sub.2) for revising chamfering or rounding is selected from a menu table (108b) of a tablet device (108), all corner portions (E.sub.1 -E.sub.3) included in profile (A.sub.1) and pertaining to the revision item (e.g., the item for revision rounding) are displayed in a color different from the other portions of the profile. Thereafter, a corner portion (E.sub.1) requiring revision is designated by a graphic cursor (K), whereupon the corner portions (E.sub.2, E.sub.3) other than the designated corner portion return to the original color so that only the designated corner portion (E.sub.1) may be identified for revision. .