Gas generator

A gas generator (1) includes, an igniter assembly (40) having an igniter (30) and an igniter collar member (10) supporting the igniter (30), a gas generating agent (50) which generates a gas when ignited by an activation of the igniter (30), and a cup-like member (20) that accommodates the gas generating agent (50), the cup-like member (20) including a side wall portion (23), an open end portion (21), and a closed end portion closed by a bottom wall, the open end portion being provided with a joining portion (22) attached to the igniter collar member (10), such that the cup-like member is integrally attached to the igniter assembly, a strength of the joining portion being greater than a strength of the side wall portion.