SEAM FORMING DEVICE, AND SEAM FORMING METHOD

To provide a seam of attractive appearance in which tightening force is increased and raveling are prevented drastically. A seam (1) is formed by two needles (11, 12) juxtaposed in the direction at substantially right angles to the sewing direction (T), and consists of a chain seam (10) formed by a needle thread (12) passed through one needle (11), and a lock seam (20) formed by a needle thread (22) passed through the other needle (21). The loop (13) of a needle thread forming the chain seam (10) is passed through the loop (23) of a needle thread forming the lock seam (20) before tightening of stitch is performed, and a loop of the needle thread forming the chain seam located on a downstream side in the sewing direction is passed through the loop of the needle thread forming the upstream chain seam.