An airbag apparatus that prevents a reverse flow of a gas between chambers to allow internal pressures of the chambers to be maintained. The airbag apparatus includes: a cushion portion with a divided internal space including a first chamber and a second chamber; a deflector surrounds a periphery of an inflator with a first gap therebetween to cover a gas ejection port of the inflator. The deflector has a first end portion projecting in a longitudinal direction and forming a space between the first end portions of the deflector and the inflator. A cloth cylindrical member surrounds a periphery of the deflector with a second gap therebetween. The cylindrical member projects from the first end portion of the deflector by a predetermined length so as to allow the first gap and the second gap to be covered in the first end portion side of the deflector.