PURPOSE: To simplify a piping system, to reduce a cost, and to ensure a seal function by providing a single switching valve with a function to switch communication between the turbine outlet side of a small capacity turbo supercharger and the turbine inlet side of a high capacity turbo supercharger and between the turbine outlet side and the exhaust pipe side and the function of a waist gate valve.

CONSTITUTION: A switching valve 14 is disposed in a communication pipe 13 through which the turbine outlet 102 of a small capacity turbo supercharger 10 and the turbine inlet 111 of a high capacity supercharger 11 is inter connected. The switching valve 14 consists of a mushroom valve 16 energized to one valve seat through the force of a compression spring 18. When the exhaust gas pressure on the turbine inlet 111 side of the high capacity turbo supercharger 11 is increased to a value exceeding a given value, the mushroom valve 16 is opened from one valve seat against the spring force of the spring 18.