A gas generator includes, a tubular housing, an ignition device attached to one end and a diffuser having a gas discharge port, attached to the other end of the housing, a tubular member, having first and second ends, disposed inside the housing such that the first and second ends are oriented towards the ignition device side and the diffuser side, respectively, and forming a tubular gap leading to the gas discharge port, a combustion chamber provided inside the tubular member, first and second gas passage holes formed on the first and second end sides, respectively, and an opening portion formed between the first and second gas passage holes, such that the gas passage holes and the opening portion communicate the combustion chamber with the tubular gap, and a projecting portion projecting from the opening portion into at least one of the combustion chamber and the tubular gap.