An air bag provided with linear joined portions in the inflation section is disclosed. The linear joined portions linearly join the opposing wall portions of the inflation section. Each of the linear joined portions, includes a body portion and end portions. The end portions extend from the body portion and gradually become wider than the body portion. The periphery surrounds the end portions and is provided with at least three straight portions. This air bag restrains mesh spreading and inflating gas leakage from the vicinity of any of the end portions of the linear joined portions. <IMAGE>
