Abstract: A gas generator, including an igniter, a gas generating agent ignited by the igniter and generating gas by burning, and a holder and an AC cup forming therein a gas generating agent storage chamber filled with the gas generating agent. A housing formed of the holder and the AC cup is vertically held and fixed by a pair of plate-like members arranged parallel with each other. The gas generator also includes projections forming deformable areas which are deformed in a direction for decreasing the vertical outside dimensions of the gas generator when the housing is fixed by the pair of plate-like members. Thus, when the gas generator is fixed by the pair of plate-like members in the vertical direction, the dispersion of the outside dimensions of the gas generator can be absorbed.