Disclosed herein is a structure of an inflater inside cylinder for an air bag for a vehicle, which lengthens the discharge course for gas generated from the inflater inside cylinder, thus preventing injury or damage due to high-temperature and high-pressure gas, and which is convenient to manufacture, is light, and has a low manufacturing cost thereof. According to the present invention, the air bag includes an outside cylinder and an inside cylinder, each having in a circumferential surface thereof a plurality of holes. In this case, the inside cylinder includes at least two cylindrical embossed steel plates, the plurality of holes being formed in embossed parts of the cylindrical embossed steel plates, which protrude outward or inwards from circumferential surfaces of the embossed steel plates so as to extend a gas discharge course. A mesh net is provided between the at least two cylindrical embossed steel plates.