In the present invention, it is an assignment to optimize a loading density of noble metal on catalyst.Pt is loaded in such an amount that a loading amount per 1 liter of a support substrate exceeds 0.75 g on an exhaust-gas upstream side of a coating layer, and a loading density of Rh in the coating layer is made so that it becomes higher on an exhaust-gas downstream side than on the exhaust-gas upstream side. The purifying performance after warming up improves by loading Rh with high density on the exhaust-gas downstream side that is likely to become rich atmosphere.