A main particulate filter having a relatively large volume is arranged in an exhaust passage of an engine, and an auxiliary particulate filter having a relatively small volume is arranged in the exhaust passage upstream of the main particulate filter. The main and auxiliary particulate filters are arranged so that the open downstream ends of the single open end-type exhaust gas passages of the auxiliary particulate filter and the open upstream ends of the open upstream end-type exhaust gas passages of the main particulate filter substantially face each other, and the open downstream ends of the both open end-type exhaust gas passages of the auxiliary particulate filter and the closed upstream ends of the open downstream end-type exhaust gas passages of the main particulate filter substantially face each other. A catalyst having an oxidation function is carried on the auxiliary particulate filter.