A device includes a first catalyst 41 including a Pd-containing catalyst layer and a Rh-containing catalyst layer and a second catalyst 42 containing Pt-loaded alumina and containing neither Rh nor Pd. The first catalyst or the second catalyst are disposed in one place in such a manner that one of the first catalyst 41 or the second catalyst 42 is located upstream of the other in a flow direction of an exhaust gas from an engine 1.