The airbag apparatus includes an airbag having a tether including an occupant side tether belt and a vehicle body side tether belt. An intermediate portion of the vehicle body side tether belt is held at the side of a housing of the airbag by a retaining mechanism. At full inflation of the airbag, the clearance between the side of the housing and the occupant side tether belt is reduced when the vehicle body side belt is retained by the retaining mechanism whereas the clearance is enlarged when the vehicle body side tether belt is released from the retaining mechanism. The occupant side tether belt and the vehicle body side tether belt are linked with each other so that a central area of a protection plane of an occupant side wall of the airbag in the former case is generally parallel to the central area in the latter.