[Problem] To feed a needle thread, an upper looper thread, and a lower looper thread in the amount necessary for sewing one stitch and such that the position of a stitch looping point of said threads changes. [Solution] The present invention includes: a thread accumulator (500) having thread accumulating elements (13a-13d, 14a-14d), each of which measures predetermined thread accumulation length for the needle thread, upper looper thread, and lower looper thread, and thread accumulation amount control elements (15-18), each of which releases a sewing thread to a stitch forming device during stitch forming and in which said needle, upper looper, and lower looper threads, in terms of the amount necessary for sewing one stitch, are adjusted to be increasable and decreasable within the range of the predetermined thread accumulation length during cloth feeding; a thread feed drive mechanism (600) that drives each of these elements; and a thread feed control unit that has a program which drives the thread accumulation amount control elements for every stitch, feeds the threads so that they are increasable and decreasable, and increases and decreases the amount of said threads relative to each other within the range of the total amount of threads to be fed (given an unchanging state including the amount of cloth to be fed, cloth thickness, and stitch width) to vary the position of the looping point of the needle, upper looper, and lower looper threads and thereby control decorative stitching using a decorative stitching pattern.
展开▼
