The present invention provides a gas generator including an ignition device chamber provided with the ignition device, a gas inflow chamber provided with a gas discharge port, and a pressurized gas chamber being arranged in order from the first end; a closing member including a fixing portion and a rupturable plate fixed to the fixing portion and closing between the pressurized gas chamber and the gas inflow chamber; and a breaking device for the rupturable plate being arranged between the ignition device chamber and the gas inflow chamber, the breaking device including a base portion, which has an outer circumferential surface abutted against an inner circumferential wall surface of the cylindrical housing, and a rod extending from the base portion to the rupturable plate, the fixing portion of the closing member including an annular plate surface portion, extending radially inward from the inner circumferential wall surface of the cylindrical housing, and a cylindrical wall portion extending from an inner circumference of the annular plate surface portion towards the gas inflow chamber, the rupturable plate of the closing member being fixed by welding to the annular plate surface portion of the fixing portion from the pressurized gas chamber, the breaking device being disposed such that a tip end of the rod is enclosed by the cylindrical wall portion of the fixing portion of the closing member.