PURPOSE: To obtain a reliable air bag which does not bring twisted parts, by synchronizing the sewing speed of two needles, while putting both sewing edges in order and guiding the sewed cloth so as to return it to the upper or the lower side of the needle to make it to form a bag in one sewing process.

CONSTITUTION: A sewing machine is provided with a pair of synchronously movable sewing needles 12, 22 arranged to make right angles with the proceeding direction of a cloth. A groove 30 dropping the cloths of both sides 42, 43 is formed between both sewing needles 12, 22 along the feeding direction of the cloth, on sewing bases 13, 23 placing each cloth. A drop guide 31 to conduct the sewed-up part of the cloths 42, 43 into the groove 30 is formed in the groove. The cloths 42, 43 of both sides dropped in the groove 30 are pulled up previously on the sewing bases 13, 23 respectively before sewing and the sewing edges of the cloths 42, 43 of both sides pulled up are put in order and the sewing edges are sewed by both sewing needles 11, 21 at the same time. In this way, an air bag is sewed to form a bag by one sewing process.