Abstract: Heat-resistant filters 6, 7 are disposed at the upstream side of a catalyst bed 9. These heat-resistant filters 6, 7 perform filtration to completely catch and remove the smoke particles suspended by the exhaust gas, so that the undesirable attaching of the smoke particles to the catalyst bed 9 is fairly avoided. Also, means are provided to regenerate the heat-resistant filters simply by burning the smoke particles attaching to these filters. In another embodiment, a heat-resistant filter 24 and a catalyst bed 26 are shaped to have hollow cylindrical forms and are superposed to each other. For regenerating the heat-resistant filter 24, hot air is introduced into the filter 24 by the action of a high pressure burner 28 or a vacuum generating section 33. The heat-resistant filter 24 and the catalyst bed 26 are accomodated by a single case 21.