The present invention provides a gas generator for an occupant restraining device of a vehicle, comprising a substantially cup-like shaped diffuser shell having a plurality of gas discharge ports on a circumferential wall portion, a substantially cup-like shaped closure shell combined with the diffuser shell to form an outer container, a housing formed by the diffuser shell and closure shell, an ignition device, a gas generating agent ignited and combusted by activation of the ignition device to generate a combustion gas, and a substantially cylindrical filter for purifying and cooling the combustion gas generated from the gas generating agent, all accommodated in the housing, the housing formed by inserting part of an outer peripheral surface in the open portion side of the closure shell into part of the inner peripheral surface of the open portion side in the diffuser shell to abut against each other, so that they are integrated, the filter supported by abutting one end surface thereof against a ceiling surface of the diffuser shell and abutting the other end surface thereof against at least an annular end surface of the open portion of the closure shell, an annular space provided between the circumferential wall having the gas discharge ports of the diffuser shell and an outer circumferential surface of the filter.