A partitioning member for dividing a connecting pipe into at least two exhaust passageways is provided in the connecting pipe, which is attached to an exhaust side of a silencer. A valve mechanism is operable to vary the passageway area of one of the exhaust passageways. With this structure, for example, when an engine is rotating at low revs, exhaust gas is discharged from the exhaust passageway without the valve mechanism, while when the engine is rotating at high revs exhaust gas is simultaneously discharged from the exhaust passageway having no valve mechanism and a passageway provided with the valve mechanism. Therefore, it is possible to reduce exhaust noise when the engine is rotating at low revs.