An airbag is formed from fabric layers joined at a seam, and gas generator inflates the airbag by means of gas expelled from the gas generator's insertion end which has been inserted into the airbag. A gas guide is formed in the airbag in order to direct gas from the gas generator into the airbag and includes a pouch-shaped gas guide member in which are formed gas injection nozzles and an attachment orifice. The insertion end of the gas generator is inserted into the attachment orifice with the gas injection nozzles facing an interior of the airbag. A convex-shaped seam is included where the fabric layers are joined, and is disposed in opposition to the gas guide member. The gas guide member comes into contact with the convex-shaped seam as a result of the pressure of the flow of gas from the gas generator through the gas guide member.