To prevent deterioration of an exhaust emission control device or a heat energy recovery device caused by overheat, and to increase noise reduction effect.

In an exhaust system 1, the exhaust emission control device or heat energy recovery device 8 are installed to a branch passage 7 which is branched from an exhaust passage 4, and an open/close valve 9 is disposed to the exhaust passage 4 to make exhaust gas selectively flow into either the exhaust passage 4 or branch passage 7. The branch passage 7 is branched at a upstream branch section 5 from the exhaust passage 4 through which the exhaust gas flows, and is united at a downstream branch section 6 to the exhaust passage 4. The exhaust emission control device or the heat energy recovery device 8 is disposed in the middle of the branch passage 7, the open/close valve 9 is disposed to the exhaust passage 4 between the upstream branch section 5 and downstream branch section 6, and a capacity chamber 10 communicating with the exhaust passage 4 is serially disposed in the middle of the exhaust passage 4 upstream of the upstream branch section 5.