A gas generator includes, a housing, an ignition device chamber, a combustion chamber, a filter facing a top plate of the housing, and a retainer supporting the filter and having first and second retainers. The first retainer includes a filter support abutting a lower surface of the filter, an annular wall positioned at outer circumference of the filter support, a plate portion extending outward from the annular wall, and a tubular wall extending axially from the plate portion, and the second retainer includes a support surface supporting the outer circumferential surface, and a support bottom extending inward from the support surface. The support bottom is positioned between the plate portion and the lower surface and that an inner circumferential edge of the support bottom abuts the annular wall surface. At least a part of the lower surface and the outer circumferential surface is supported by the first and second retainers.