A gas generator for a restraining device comprising: a cylindrical housing having an ignition device provided at one end in a long-axis direction thereof and a diffuser portion including a gas discharge port provided at the other end thereof; a gas generating agent charged in an inner space of the housing; characterized in that the gas generator for a restraining device is further comprising: a plate-like partition member, having a communication hole, disposed, in an inner space of the cylindrical housing, so as to incline relative to a long axis of the cylindrical housing, thereby dividing the inner space into two mutually adjacent spaces, that is, a gas generating agent charging space and a gas flow channel space, the gas flow channel space communicating with the diffuser portion, both of side edges of the plate-like partition member being abutted against an inner circumferential surface of the cylindrical housing, a cross-sectional area of the gas generating agent charging space in a short-axis direction perpendicular to the long axis decreasing from a side of the ignition device toward a side of the diffuser portion, a cross-sectional area of the gas flow channel space in the short-axis direction increasing from a side of the ignition device toward a side of the diffuser portion. a cylindrical housing having an ignition device provided at one end in a long-axis direction thereof and a diffuser portion including a gas discharge port provided at the other end thereof; a gas generating agent charged in an inner space of the housing; characterized in that the gas generator for a restraining device is further comprising: a plate-like partition member, having a communication hole, disposed, in an inner space of the cylindrical housing, so as to incline relative to a long axis of the cylindrical housing, thereby dividing the inner space into two mutually adjacent spaces, that is, a gas generating agent charging space and a gas flow channel space, the gas flow channel space communicating with the diffuser portion, both of side edges of the plate-like partition member being abutted against an inner circumferential surface of the cylindrical housing, a cross-sectional area of the gas generating agent charging space in a short-axis direction perpendicular to the long axis decreasing from a side of the ignition device toward a side of the diffuser portion, a cross-sectional area of the gas flow channel space in the short-axis direction increasing from a side of the ignition device toward a side of the diffuser portion. a plate-like partition member, having a communication hole, disposed, in an inner space of the cylindrical housing, so as to incline relative to a long axis of the cylindrical housing, thereby dividing the inner space into two mutually adjacent spaces, that is, a gas generating agent charging space and a gas flow channel space, the gas flow channel space communicating with the diffuser portion, both of side edges of the plate-like partition member being abutted against an inner circumferential surface of the cylindrical housing, a cross-sectional area of the gas generating agent charging space in a short-axis direction perpendicular to the long axis decreasing from a side of the ignition device toward a side of the diffuser portion, a cross-sectional area of the gas flow channel space in the short-axis direction increasing from a side of the ignition device toward a side of the diffuser portion.