A gas generator (10; 100; 200) comprising: an igniter having an ignition portion and a conductive pin; a collar holding the igniter, a metallic cup-shaped case (40; 140) fixed to the collar and having a fragile portion, and charged therein with a gas generating agent, the collar being formed by integrating a metallic portion (21; 121) and a resin portion (25; 125), and the resin portion (25; 125) having a resin columnar part (26; 126) enclosing at least part of a peripheral surface of the ignition portion, the metallic portion (21; 121) being in a substantially cup-like shape having an annular bottom surface part (22; 122) and a circumferential wall (23; 123), and an outer diameter of the circumferential wall (23; 123) being set to be larger than an outer diameter of the resin columnar part (26; 126), the cup-shaped case (40; 140) having an annular bent portion (45; 145) obtained by bending inward an end portion of an opening thereof, the annular bent portion (45; 145) including an annular bent corner (48; 148), an annular tilted surface (47; 147), and an annular terminal end (46; 146), and the annular tilted surface (47; 147) including an outer annular tilted surface (47b; 147b) facing toward a side of a peripheral surface of the cup-shaped case (40; 140) and an inner annular tilted surface (47a; 147a) facing the opposite side thereof, in the cup-shaped case (40; 140) and the collar, the inner annular tilted surface (47a; 147a) of the annular bent portion (45; 145) pressing against a peripheral surface of the columnar part (26; 126) of the resin portion (25; 125), characterized in that the resin columnar part (26; 126), to which the inner annular tilted surface (47a; 147a) is in press-contact, has a uniform outer diameter such that the peripheral surface of the resin columnar part (26; 126) on a bottom surface side has no protrusion, step or part having an enlarged outer diameter. an igniter having an ignition portion and a conductive pin; a collar holding the igniter, a metallic cup-shaped case (40; 140) fixed to the collar and having a fragile portion, and charged therein with a gas generating agent, the collar being formed by integrating a metallic portion (21; 121) and a resin portion (25; 125), and the resin portion (25; 125) having a resin columnar part (26; 126) enclosing at least part of a peripheral surface of the ignition portion, the metallic portion (21; 121) being in a substantially cup-like shape having an annular bottom surface part (22; 122) and a circumferential wall (23; 123), and an outer diameter of the circumferential wall (23; 123) being set to be larger than an outer diameter of the resin columnar part (26; 126), the cup-shaped case (40; 140) having an annular bent portion (45; 145) obtained by bending inward an end portion of an opening thereof, the annular bent portion (45; 145) including an annular bent corner (48; 148), an annular tilted surface (47; 147), and an annular terminal end (46; 146), and the annular tilted surface (47; 147) including an outer annular tilted surface (47b; 147b) facing toward a side of a peripheral surface of the cup-shaped case (40; 140) and an inner annular tilted surface (47a; 147a) facing the opposite side thereof, in the cup-shaped case (40; 140) and the collar, the inner annular tilted surface (47a; 147a) of the annular bent portion (45; 145) pressing against a peripheral surface of the columnar part (26; 126) of the resin portion (25; 125), characterized in that the resin columnar part (26; 126), to which the inner annular tilted surface (47a; 147a) is in press-contact, has a uniform outer diameter such that the peripheral surface of the resin columnar part (26; 126) on a bottom surface side has no protrusion, step or part having an enlarged outer diameter.