An airbag apparatus may include: a first chamber connected to an inflator, and supporting the head of a passenger in case of a head-on collision of a vehicle; a second chamber connected to one side of the first chamber, expanded toward the rear of the vehicle, and suppressing the head of the passenger from moving in a diagonal direction based on the front of the vehicle, in case of an oblique collision of the vehicle; a tube part coupled to the first chamber to introduce gas of the first chamber into the second chamber, and having a ring-shaped tightening part formed along the circumference thereof; and a tether part having one end coupled to the first chamber and the other end passed through the tightening part, and closing the tube part after the first chamber is completely deployed.