PURPOSE: To prevent a damage on a scavenging valve and reduce a pressue loss by making up a part or all part of a valve plate of the scavenging valve and connecting a scavenging trunk between the scavenging valve and an engine.

CONSTITUTION: A scavenging duct 2 connects an exhaust trunk 11 to exhaust turbosupercharger 1 which directly combines an exhaust turbine 1a with a comressor 1b. A valve plate 9 of an exhaust valve 8 is made up of a bimetal 9a and an auxiliary blower 5 is disposed outside of a scavenging duct 2. As the temperature of an exhaust gas grows higher, the valve plate 9 is moved more away from a valve seat 10 to reduce a vibration caused by a flowing air and an impact given by it on the valve seat 10, thereby preventing a damage resulting from a fatigue of the valve plate 9. In the normal operation, the scavenging valve 8 is fully opened so that a pressure loss may be reduced.