An airbag apparatus for an automobile includes an airbag case for accommodating an airbag in a folded condition, the airbag case being disposed behind a surface panel which is made of a thermoplastic resin material and provided within the automobile; a fracture-opening section of the surface panel, the fracture-opening section facing an opening of the airbag case and being defined by means of fracture grooves formed on an inside surface of the surface panel; at least one reinforcement plate member fixed to the inside surface of the surface panel in a region corresponding to the fracture-opening section; and a frame member surrounding the reinforcement plate member and fixed to the inside surface of the surface panel in a region surrounding the fracture-opening section. The frame member and the reinforcement plate member are each made of a thermoplastic resin material, and are fixed to the inside surface of the surface panel through vibration welding.