In a computerized sewing machine, initial coordinate values of amplitudes of needle drops (the stitching width) for line-and bar tacks of a buttonhole are stored in a ROM. Desired stitching amplitude values and cut width values are selected by external setting means on the machine and stored in a RAM. The stored desired data are adjusted to coordinates of the present initial values in such a manner that selected needle drop or stitching amplitude values are offset in parallel relative to a center value of a maximum stitching amplitude available in the machine. The widths of stitches of the left-and right line tacks remain unchanged for different cut widths of a buttonhole and only the amplitudes of the bar tack stitches are adjusted to a particular cut width.