An air bag having light weight and a flexibility, capable of being stored more compactly, highly durable with respect to a load during an operation thereof and long-term aging, and formed of a bag body of two pieces of woven fabric comprising polyamide synthetic fibers containing 30-200 ppm copper compound in terms of copper, or a three-dimensionally and properly formed cut cloth, characterized in that the woven fabrics have a product of a total fineness of weft yarn or warp yarn and fabric density of not more than 1600 decitex.number of yarns/2.54 cm, a load at an elongation percentage of 15 % of 3-35 N/%/2.54 cm, and an extension breakage work volume before the occurrence of breakage of 7000-30000 N.%/2.54 cm. This air bag can be used as any one of an air bag for driver's seat of an automobile, an air bag for an assistant driver's seat thereof and a side air bag thereof.