A gas generator, comprising: a housing forming an outer shell and including a top plate, a bottom plate and a circumferential wall (13, 16) provided with a gas discharge port; in the housing, an ignition device chamber provided in the housing and defined by a cylindrical container which has one end closed, and accommodating an ignition device; a combustion chamber formed to surround the ignition device chamber and charged with a gas generating agent; an annular or disk-shaped filter arranged to face the top plate and form a gap with the circumferential wall; and an annular retainer supporting the filter, the annular retainer being formed by a combination of a first retainer and a second retainer, characterized by the first retainer including a filter support portion being formed by an annular flat-plate and abutting against a lower surface of the filter, an annular wall surface portion positioning at outer circumference of the filter support portion and extending towards the bottom plate, an annular flat-plate portion extending radially outward from the annular wall surface portion, and a tubular wall portion extending axially from the annular flat-plate portion and being fixed to the circumferential wall (13,16) of the housing, and the second retainer including, a tubular support surface portion supporting an outer circumferential surface of the filter, and an annular support bottom portion extending radially inward from the tubular support surface portion, the first retainer and the second retainer being combined such that the annular support bottom portion of the second retainer positions between the annular flat-plate portion of the first retainer and the lower surface of the filter and that an inner circumferential edge of the annular support bottom portion of the second retainer abuts against the annular wall surface portion, at least a part of the lower surface and the outer circumferential surface of the filter being supported by the combination of the first retainer and the second retainer. a housing forming an outer shell and including a top plate, a bottom plate and a circumferential wall (13, 16) provided with a gas discharge port; in the housing, an ignition device chamber provided in the housing and defined by a cylindrical container which has one end closed, and accommodating an ignition device; a combustion chamber formed to surround the ignition device chamber and charged with a gas generating agent; an annular or disk-shaped filter arranged to face the top plate and form a gap with the circumferential wall; and an annular retainer supporting the filter, the annular retainer being formed by a combination of a first retainer and a second retainer, characterized by the first retainer including a filter support portion being formed by an annular flat-plate and abutting against a lower surface of the filter, an annular wall surface portion positioning at outer circumference of the filter support portion and extending towards the bottom plate, an annular flat-plate portion extending radially outward from the annular wall surface portion, and a tubular wall portion extending axially from the annular flat-plate portion and being fixed to the circumferential wall (13,16) of the housing, and the second retainer including, a tubular support surface portion supporting an outer circumferential surface of the filter, and an annular support bottom portion extending radially inward from the tubular support surface portion, the first retainer and the second retainer being combined such that the annular support bottom portion of the second retainer positions between the annular flat-plate portion of the first retainer and the lower surface of the filter and that an inner circumferential edge of the annular support bottom portion of the second retainer abuts against the annular wall surface portion, at least a part of the lower surface and the outer circumferential surface of the filter being supported by the combination of the first retainer and the second retainer.