Provided is an airbag which can be easily manufactured though it is provided with a tether inside, and has a reduced fear of gas leakage from a joint region. The airbag includes a joint region of outer circumferential edges of a pair of walls. The joint region includes, between the outer circumferential edges of the pair of walls, a sealing member which has elasticity, and has adhesiveness in an unsolidified state. The joint region is formed by such a sewing that runs a sewing thread through an application area of the sealing member. A tether connects the pair of walls. The joint region includes a region in which the sealing member has a solidified, thus non-adhesive surface, and is pressed against at least one of the walls by the non-adhesive surface, and penetrated by the sewing thread in that state.