In the air bag device, a bag holder, a retainer, and an air bag can be assembled together into a united body by use of bolts and nuts which are provided so as to extend from a retainer formed from a metal plate. At a plurality of positions near a peripheral edge of an opening formed in the air bag, there are formed insertion holes. In the retainer, there are provided a plurality of securing projections which are inserted through associated insertion holes and into associated securing holes formed in the bag holder. Each of the securing projections is cut and raised from a main body of the retainer and has a semi-cylindrical shape with the peripheral wall thereof raised from the retainer and a semi-arc shaped outer peripheral surface of the peripheral wall faces the opening of the air bag.