GAS GENERATOR

A gas generator (1A) includes a partition portion (32), a cylindrical portion (41), and a separation wall portion (51) which divide a space in a housing into a first combustion chamber (S1A), a second combustion chamber (S1B), a gas passage chamber (S2), and a gas emission chamber (S3). The first combustion chamber (S1A) includes a space inside the cylindrical portion (41) on a side of an igniter (22) relative to the separation wall portion (51), and the second combustion chamber (S1B) includes the space inside the cylindrical portion (41) on a side of the partition portion (32) relative to the separation wall portion (51). The gas passage chamber (S2) includes a space outside the cylindrical portion (41) which faces a circumferential wall portion (11) of the housing, and the gas emission chamber (S3) includes a space on a side of a gas discharge opening (13) relative to the partition portion (32). At least some of a gas generated in the first combustion chamber (S1A) at the time of activation of the gas generator (1A) is emitted to the outside sequentially through the gas passage chamber (S2), the second combustion chamber (S1B), and the gas emission chamber (S3).