An original picture of a pattern is scanned with an image scanner to obtain bitmap image data. A border line defining the original picture is extracted. A closed region enclosed by the border line is subjected to a linearizing process. Shape-defining line data is produced for the closed region and stitch data for entirely covering the closed region with zigzag stitches when the closed region can completely be linearized by a number of sequential pixel deleting cycles not greater than a given number. Border line data is produced and stitch data for entirely covering the closed region with satin stitches is automatically produced when the closed region could not be completely linearized by the number of sequential pixel deleting cycles within the given number. Thus, stitch data for satisfactorily embroidering a pattern consisting of a plurality of partial patterns respectively having different widths can be readily and automatically produced from the original picture of the pattern.