An airbag apparatus includes: a first left chamber that is expandable so as to cover an outer surface of a front left pillar which is located on a left side with respect to a vehicle width direction of a vehicle; a second left chamber that is expandable on the first left chamber; a first right chamber that is expandable so as to cover an outer surface of a front right pillar which is located on a right side with respect to the vehicle width direction of the vehicle; a second right chamber that is expandable on the first right chamber; and a gas supply unit that supplies a gas for expansion selectively to the first left chamber, the second left chamber, the first right chamber, and the second right chamber.