An airbag is expanded upward on the side of a passenger from a door part. A cover body which covers the airbag is formed by overlaying an outer part made of a hard resin to an inner part made of a soft resin. A supporting piece part is protruded from the cabin external side of the inner part. A to-be-ripped part is formed on the supporting piece part. On expansion of the airbag, the to-be-ripped part is ripped, thereby allowing the door part to move rotationally on the cabin internal side. Therefore, the airbag equipped at the door part can be smoothly expanded along the side face part of the cabin. Thus, an airbag apparatus is improved in appearance.