PURPOSE: To realize the exhaust emission control of an engine capable of sufficiently controlling the exhaust gas without deteriorating the output performance.

CONSTITUTION: A double-walled structure consisting of an inner wall tube 10 having an inner space 14 which is smoothly connected to an exhaust passage on the upstream side and an outer wall tube 15 covering the outside of this inner wall tube 10 is formed on a part of the exhaust passage 14 to flow the exhaust gas G of the engine. An exhaust gas controlling catalyst 13 is carried by at least the inner circumferential surface of the inner wall tube 10. An introducing hole 17 to introduce the exhaust gas G into the space 16 between the inner wall tube 10 and an outer wall part 15a is formed preferably in the end part on the upstream side of the exhaust gas in the inner wall tube 10. Further preferably, an introducing part 19 to introduce the exhaust gas into the introducing hole 17 is formed in an edge part of the introducing hole 17 in a projecting manner in the exhaust passage 14.