An airbag apparatus comprised of a cover for covering an expanding side of an airbag and forming an opening for the airbag. The cover is comprised of a door portion disposed at the expanding side of the airbag, a surrounding portion surrounding the door portion, a tear portion defining the door portion and tearing due to an expansion force of the airbag, an installation portion protruding from the surrounding portion adjacent to the tear portion toward an opposite side of the expanding side, and a hinge portion connecting the door portion and the surrounding portion located outside of the installation portion.