An airbag apparatus includes a fixing bracket fixed to an upper portion of the side wall of a vehicle. The fixing bracket has an inflator support portion that supports an inflator, a fastening portion fastened and fixed to the upper portion of the side wall of the vehicle at a position below the inflator, and a restraining wall that extends along the axis direction of the fastening portion under the inflator. An airbag body is disposed between the inflator and an upper wall portion of the restraining wall, and the airbag body is compressed by the inflator and the upper wall portion and held between the inflator and the upper wall portion. The restraining wall restrains displacement of the airbag body so that the airbag body does not overlap a fastening operation area into which the fixing bracket is fastened.