A gas generator including an enhancer chamber provided on a first end of a cylindrical housing and including an igniter therein, a diffuser portion formed with a gas discharge port on a second end, a combustion chamber provided between the diffuser portion and the enhancer chamber, the enhancer chamber being an internal space which is axially sandwiched between the igniter and a cup-shaped partition wall, the internal space accommodating therein an enhancing agent, the cup-shaped partition wall including a peripheral wall provided with a peripheral wall body with a plurality of nozzles and an annular portion expanding outwardly from the peripheral wall body, an outer surface of the annular portion abutting against an inner wall surface of the cylindrical housing, a cylindrical gap being formed between the peripheral wall body and the inner wall surface, the nozzles being disposed to face the cylindrical gap, and the cylindrical gap being devoid of the gas generating agent therein.