An airbag apparatus equipped in a vehicle seat having a seat cushion that forms a seating surface and a seat back that forms a backrest includes: an inflator that generates inflation gas; and an airbag housed within at least the seat back and deployed by inflation gas released from the inflator. The airbag includes a pair of left and right side chambers that deploy towards the front from a side portion of the seat back and an upper chamber that deploys above the head of a passenger. The airbag is rolled in a direction that intersects the longitudinal direction from a flat unfolded state prior to being housed or folded to be compressed into a long bar shape. A folded portion is formed by folding at least a location corresponding to the upper chamber of the long bar shaped airbag to house the folded portion above the seat back.