An airbag apparatus includes airbag having a vent hole formed therein, an inflator configured to emit gas for inflating the airbag, and a chamber configured to accommodate the inflator therein inside the airbag, the chamber having at least one discharge aperture for discharging gas emitted from the inflator to an inside of the airbag, and having a wall part configured to guide the emitted gas to the discharge aperture, wherein an external surface of the wall part is configured to partially cover the vent hole upon collapse of the chamber toward the vent hole.