PURPOSE: To prevent the generation of noise due to the air flow noise of an air bypass valve by closing an opening/closing valve installed at the upstream side position from the communication position of a bypass passage in an intake passage on the upstream side of a compressor, in the deceleration operation.

CONSTITUTION: A bypass passage 42 allows an intake passage 12-6 on the upstream side of a compressor 6 and an intake passage 12-2 on the downstream side to communicate with each other. An air bypass valve 44 which is closed during the deceleration operation of a vehicle on which an internal combustion engine 2 is mounted is installed midway in the bypass passage 42. An opening and closing valve 64 is installed at the upstream side position from the communication position of the bypass passage 42, and this valve 64 is closed during the deceleration operation of the vehicle. Accordingly, the passage between the outside and the intake passage 12 can be shielded, and the outside liberation of the air flow noise generated in the air bypass valve 44 can be prevented.