An automotive air bag device avoids disengagement or play between the air bag activation unit and the lid, which covers the air bag inflation opening, during transportation to an automobile assembly plant and after the air bag device has been installed in a vehicle. Extending from the back surface of the lid, is an integrally formed attachment piece. The air bag activation unit has a number of hook members that engage support openings in the attachment piece. A thin, elastic tongue piece, integrally formed on the upper edge of each support opening, prevents disengagement of the hook member.