The invention provides an airbag apparatus including an airbag that is folded toward an inflator attaching part and that is accommodated within a pad functioning as a case such that the airbag is provided with first and second folded parts arranged on a cabin side from an inflator. A tear line is formed on the pad at a position deviated from a center of the inflator toward the first folded part and divides the case into a first door and a second door. In the airbag apparatus, the second folded part that is covered by the first door is folded in a bellows shape.