To provide an airbag device allowing connection release timing of a temporary connection part to be substantially constant, and ensuring stable occupant protection performance.

An airbag 25 folded and stored in a storage portion 11 has, at a part of each of outer peripheral walls 27, the temporary connection part 36 for mutually connecting the outer peripheral walls 27. During the initial expansion, the airbag expands to a small volume with the connection state by the temporary connection part 36 maintained. Before completion of the expansion, the airbag expands to a large volume upon release of the connection state by the temporary connection part 36. The temporary connection part 36 has a starting end 37a that becomes a starting point when the connection is released. The airbag 25 includes a connection member 43 extended from a portion in the vicinity of the starting end 37a. A front end 43a side of the connection member is connected to a storage portion 11 side. The connection member 43 suppresses tension exerted on the starting end 37a during the initial expansion of the airbag 25, and releases the connection with the storage portion 11 side so that the connection of the temporary connection part 36 can be released during an increase in the inner pressure of the airbag 25.