<p>A gas generator (1A) includes an elongated cylindrical housing (10), a partition plate (40) partitioning the space within the housing (10) into a gas generating agent storing chamber (16) and a filter chamber (17) in the axial direction, and an igniter (30). A filter (60) is made of a cylindrical member having a hollow portion (61) extending in the axial direction of the housing (10). The partition plate (40) includes an annular plate portion (41) covering the end face of the filter (60) closer to the gas generating agent storing chamber (16), a cylindrical portion (42) continuously extending from the inner circumferential edge of the annular plate portion (41) into the hollow portion (61) of the filter (60) to cover the inner circumferential surface of the filter (60) closer to the end face, and a communication hole (43) defined by the inner circumferential surface of the cylindrical portion (42) and providing communication between the gas generating agent storing chamber (16) and the filter chamber (17). The cylindrical portion (42) has a cross-sectional area that is changed in accordance with an increase in the distance from the annular plate portion (41). This configuration can provide a gas generator that can be reduced in size and weight and readily be manufactured without deteriorating the performance.</p>
