A gas generator (Y) capable of distributing hot gas generated at the time of initial combustion in the axial direction of a filter member so as to prevent the filter member from being thermally damaged in order to increase the slag collecting and cooling efficiencies, wherein the gas passing efficiency of the filter member (3) is differentiated in the axial direction of a housing (1), and the filter member (3) is so constructed that the shaft end part side of the housing (1) having an ignitor (5) is more difficult to pass gas therethrough than the other part side of the housing (1) leading to the other shaft end part of it.
