To improve emission control efficiency by maintaining exhaust gas temperature in appropriate temperature in an exhaust pipe of an internal combustion engine.

A double exhaust pipe 29 having an outer pipe 33 provided outside of an inner pipe 31 via a space part 32 is provided between an exhaust manifold 28 and an emission control catalyst device 30. A heat conduction member 34 made of shape memory alloy is attached on an inner circumference surface of the outer pipe 33. The heat conduction member 34 deforms according to temperature of the outer pipe 33 correlating to temperature of exhaust gas and the inner pipe 31 and the outer pipe 33 can be switched in a connection condition and a disconnection condition.