To eliminate necessity for a mechanical switching means of valve or the like, oxidizingly purify HC and SOF in a whole region ranging from a low temperature region to a high temperature region, and suppress discharge of particulate in the high temperature region.

The first exhaust gas flow path 2 storing a low temperature type oxidation catalyst 20 and the second exhaust gas flow path 3 storing a high temperature type oxidation catalyst 30 are arranged in parallel in an exhaust gas flow path of a Diesel engine 1, a pressure drop value of the first exhaust gas flow path 2 is set larger than a pressure drop value of the second exhaust gas flow path 3. Exhaust gas of high temperature region automatically preferentially flows in the second exhaust gas flow path 3 of small pressure drop value, to come into contact with the high temperature type oxidation catalyst 30. In this way, discharge of sulfate is suppressed, a temperature window is spread.