A thread hook and a looper thread holder are arranged on a rear side of a needle drop position of a sewing machine. When usual sewing is completed, the thread hook and the looper thread holder swing and move close to a looper. A hook part provided at a tip end of the thread hook holds a needle thread loop caught by the looper and positions it on an advance end side of the looper away from the needle drop position, and a thread receiving part provided at a tip end of the looper thread holder holds a looper thread extending from the looper to cloths and positions it on the front side away from the needle drop position. The sewing machine performs sewing for at least one stitch while maintaining positions of the needle thread loop and the looper thread.