The purpose of the intake system, which is disposed in a limited space above the engine, is to improve engine performance by preventing increase in both temperature and resistance of intake air, and also to reduce noise of the intake air. In the intake system, a rear wall extending downwardly is formed in a lower half body that is joined to a rear end of an engine cover, and a mounting frame section for attaching an element is formed in a rear wall section. An upstream-side casing is formed forward of the rear wall section. An intake duct has a downstream end connected to a front surface of the upstream-side casing adjacent to a transmission. Further, the intake duct extends widthwise of the vehicle and has an upstream end opened to the side edge of the engine cover adjacent to the transmission. A resonance chamber casing is joined to the side departing from the transmission through a communication pipe forward of the upstream-side casing. The resonance chamber casing is formed to extend along the full width of the engine cover so as to cover the front of the intake duct.