A continuous partition wall is formed in the air introducing duct. The air introducing duct has a length L. The partition wall has a length equal to or greater than L/2. The partition wall divides the air introducing duct into first and second sections. A resonance silencer and a connecting duct are connected to the first section. A connecting position of the resonance silencer and the connecting duct is set such that the connecting position is fully included within a partition wall positioned range. A valve is arranged in the second section. Thus, intake noises is decreased in a wide range from a low frequency about 40 Hz to an intermediate frequency about several hundred Hz, which is normally hearable.