An airbag apparatus is mounted on a vehicle as housed in a housing and includes an airbag inflatable with inflation gas for catching an object of protection. The airbag includes a sheet-shaped circumferential wall made from synthetic resin. The circumferential wall is plastically deformable in such a manner as to be elongated due to increase of internal pressure caused by being pressed by the object of protection when arresting the object of protection at full inflation.
