An airbag apparatus includes an airbag having an interior divided into a plurality of chambers, and a gas generator for inflating the airbag so that gas is guided directly to each chamber from the gas generator. Slide motion of the door is imparted by a door handle and a reaction rod which acts against a link. The opening can be covered up by the side panel, and the latch can be movably arranged on the side panel. Therefore, it is difficult to increase throughputs and productivity. Either end portion of the first case in a third direction has a first protruding portion.