Abstract: An outer housing 12 formed of a sheet metal is provided such that its open end portion 312 surrounds an outer edge portion 26 of an inner housing 11 formed by casting. An outer protrusion 216, an annular protrusion 227, and a connecting portion 27 are provided on the outer edge portion 26 of the inner housing 11. The open end portion 312 of the outer housing 12 is joined to a protruding end 217 of the outer protrusion 216, a protruding end 228 of the annular protrusion 227, and an end edge 271 of the connecting portion 27, whereby the inner housing 11 and the outer housing 12 are integrated.

Abstract: An exhaust gas receiver 21 is provided between an expanded passage portion 132 of an upstream connection member 13 and a catalyst end surface 111. The exhaust gas receiver 21 extends along the entire circumference of a catalyst accommodation case 12. The exhaust gas receiver 21 extends from an upstream opening end portion 121 of the catalyst accommodation case 12 toward an inner part of the passage of the expanded passage portion 132 such that the exhaust gas receiver 21 separates from the expanded passage portion 132, and a space 211 is defined between the exhaust gas receiver 21 and the catalyst end surface 111. Flows of bypass exhaust gas hitting against the catalyst end surface 111 and bouncing off the catalyst end surface 111 hit against and are received by the exhaust gas receiver 21.

Abstract: An outer housing 12 formed of a sheet metal is provided such that its open end portion 312 surrounds an outer edge portion 26 of an inner housing 11 formed by casting. An outer protrusion 216, an annular protrusion 227, and a connecting portion 27 are provided on the outer edge portion 26 of the inner housing 11. The open end portion 312 of the outer housing 12 is joined to a protruding end 217 of the outer protrusion 216, a protruding end 228 of the annular protrusion 227, and an end edge 271 of the connecting portion 27, whereby the inner housing 11 and the outer housing 12 are integrated.

Abstract: An exhaust gas receiver 21 is provided between an expanded passage portion 132 of an upstream connection member 13 and a catalyst end surface 111. The exhaust gas receiver 21 extends along the entire circumference of a catalyst accommodation case 12. The exhaust gas receiver 21 extends from an upstream opening end portion 121 of the catalyst accommodation case 12 toward an inner part of the passage of the expanded passage portion 132 such that the exhaust gas receiver 21 separates from the expanded passage portion 132, and a space 211 is defined between the exhaust gas receiver 21 and the catalyst end surface 111. Flows of bypass exhaust gas hitting against the catalyst end surface 111 and bouncing off the catalyst end surface 111 hit against and are received by the exhaust gas receiver 21.