A gas generator, comprising: a cylindrical housing containing a combustion chamber constituted of a top plate portion and a bottom plate portion closing axial end portions and a circumferential wall portion (12, 22) provided with a gas discharge opening and accommodating a gas generating agent; an igniter charged with an ignition agent for burning said gas generating agent; and a fixing portion fixing said igniter to said bottom plate portion, said bottom plate portion being provided with an opening, said igniter including an ignition portion defining an ignition chamber accommodating said ignition agent and a terminal pin connected to said ignition portion for igniting said ignition agent and arranged to pass through said opening, said ignition portion having a substantially cylindrical cup body having a closed upper end and an open lower end and a plug closing the lower end of said cup body and supporting said terminal pin, said fixing portion being formed from a resin molding secured to said bottom plate portion and said igniter, by attaching a fluid resin material to said bottom plate portion and said igniter so as to close said opening and solidifying the fluid resin material, and said resin molding including an annular cover portion secured to an outer circumferential surface of said cup body so as to cover the outer circumferential surface, characterized by said cup body including a contact portion located on a side of said bottom plate portion and being in contact with said plug and a non-contact portion located on a side of said top plate portion and facing said ignition chamber as not being in contact with said plug, said cover portion having a lower-side annular cover portion provided on the side of said bottom plate portion so as to cover at least a part of said contact portion and an upper-side annular cover portion provided on the side of said top plate portion so as to cover at least a part of said non-contact portion, said cover portion being formed in a stepped shape having a substantially two-dimensionally annular step-formed surface substantially orthogonal to an axial direction of said cup body, with a thickness of said upper-side annular cover portion along a radial direction being smaller than a thickness of said lower-side annular cover portion along the radial direction, and said step-formed surface being located flush with a boundary surface between said contact portion and said non-contact portion or located on the side of said bottom plate portion relative to said boundary surface along an axial direction of said housing. a cylindrical housing containing a combustion chamber constituted of a top plate portion and a bottom plate portion closing axial end portions and a circumferential wall portion (12, 22) provided with a gas discharge opening and accommodating a gas generating agent; an igniter charged with an ignition agent for burning said gas generating agent; and a fixing portion fixing said igniter to said bottom plate portion, said bottom plate portion being provided with an opening, said igniter including an ignition portion defining an ignition chamber accommodating said ignition agent and a terminal pin connected to said ignition portion for igniting said ignition agent and arranged to pass through said opening, said ignition portion having a substantially cylindrical cup body having a closed upper end and an open lower end and a plug closing the lower end of said cup body and supporting said terminal pin, said fixing portion being formed from a resin molding secured to said bottom plate portion and said igniter, by attaching a fluid resin material to said bottom plate portion and said igniter so as to close said opening and solidifying the fluid resin material, and said resin molding including an annular cover portion secured to an outer circumferential surface of said cup body so as to cover the outer circumferential surface, characterized by said cup body including a contact portion located on a side of said bottom plate portion and being in contact with said plug and a non-contact portion located on a side of said top plate portion and facing said ignition chamber as not being in contact with said plug, said cover portion having a lower-side annular cover portion provided on the side of said bottom plate portion so as to cover at least a part of said contact portion and an upper-side annular cover portion provided on the side of said top plate portion so as to cover at least a part of said non-contact portion, said cover portion being formed in a stepped shape having a substantially two-dimensionally annular step-formed surface substantially orthogonal to an axial direction of said cup body, with a thickness of said upper-side annular cover portion along a radial direction being smaller than a thickness of said lower-side annular cover portion along the radial direction, and said step-formed surface being located flush with a boundary surface between said contact portion and said non-contact portion or located on the side of said bottom plate portion relative to said boundary surface along an axial direction of said housing.