An intake manifold is located on a downstream side of a throttle valve in an intake passage. A switching valve is placed on an upstream side of a connection between a communication conduit and an outlet of a lower portion of a surge tank of the intake manifold and is adapted to open or close the communication conduit. A control device controls the switching valve to open or close the switching valve. The control device closes the switching valve when an operational state of an engine is in one of idling time, accelerating driving time and high speed driving time of a vehicle, and the control device opens the switching valve when the operational state of the internal combustion engine is in decelerating driving time of the vehicle.