To provide a structure automatically discharging, to the outside, stagnated water causing a reduction in muffling effect by the stagnated water in a silencer and the corrosion of a muffler.

A thin pipe 6 connecting an exhaust gas flow 4 to the stagnated water 5 is installed at the rear lower part of the silencer 2. The thin pipe 6 is installed so as to extend from near the rear bottom part of the silencer 2 to the diameter inner side of an exhaust port pipe 3 which is the outlet of a main passage for exhaust gas. The stagnated water 5 is sucked by the spraying effect and the gas pressure of exhaust gas flow, and automatically discharged to the outside together with the exhaust gas flow 4.