An airbag is folded into a predetermined shape and is held by a shape-maintaining member or rubber strap to keep its shape. Both ends of the rubber strap are attached to the airbag by sewing portions. When the airbag is inflated with gas from an inflator, the rubber strap is detached, so that the airbag rapidly expands. In the airbag device with the shape-maintaining member, the shape of the folded airbag can be maintained, so that the airbag can be easily assembled.