PURPOSE: To make the arrangements of hoses for air bypass from an air bypass valve(ABV) easier, and the connection and disconnection of an ABV chamber easier, by providing the ABV to an intercooler outlet pipe, and the ABV chamber at the position at the upper part of an engine mechanism.

CONSTITUTION: The pipes as air passages are arranged to feed the air to a supercharger 14 from an intake pipe 12a, and after cooling in an intercooler 16, to pass the air through an intercooler outlet pipe 18, a throttle body 20, and a surge tank 22, and then to feed to each cylinder of an engine main body 10 from an intake maniford 24. And an excessive air passage from an ABV 2 provided at the lower side of the intercooler outlet pipe 18 is arranged to let flow from the ABV 2 to the upper side, passing through an air bypass hose 8 provided along the intercooler outlet pipe 18, to let flow in an ABV chamber 6 at the upper side of a surge tank 22, and to return to the intake pipe 12a after passing through the air bypass hose 8.