To improve warm-up performance of a catalyst device when exhaust gas temperature is in a low temperature range, and suppress thermal degradation of the catalyst device when exhaust gas temperature is in a high temperature range.

An exhaust pipe 20 is arranged between an internal combustion engine and the catalyst device for purifying exhaust gas. The exhaust pipe 20 has a first route R1, a second route R2 defined in the first route R1, and a valve system 33 for opening and closing the first route R1 and the second route R2. The valve system 33 closes the first route R1 and opens the second route R2 when exhaust gas temperature is in a low temperature range, and opens the first route R1 and partly closes the second route R2 when exhaust gas temperature is in a high temperature range.