Abstract: The present invention relates to a gas generator for an air bag, comprising, in a housing having a gas discharge port, a combustion chamber, and the combustion chamber accommodating a gas generating agent that generates gas by combustion and an ignition device for igniting and combusting the gas generating agent, the ignition device being formed by integrating an electric igniter and a substantially cylindrical igniter collar with a resin in a state where the electric igniter is disposed inside the igniter collar, the ignition device being in contact with the bottom surface of the housing in at least part of the surface of the igniter collar and being attached on the housing bottom surface by at least one from the following attachment structures (1) to (3): (1) The igniter collar is fixed by a support member having a flat section and a tubular section extending upward from the flat section, the flat section is fixed to the housing bottom surface, and the upper end surface of the igniter collar is pressed and