To provide an intake system without generation of noise at a point where intake air of a by-pass passage meets a main passage and without engine malfunction and output malfunction due to air suction shortage in an initial idling state of the engine.

Noise is prevented by forming a discharge port 22 of the by-pass passage so that it meets the main passage 20 of the surge tank with specified inclination against the main passage 20. The engine malfunction and output malfunction at the time of idle driving is prevented by extending output of the by-pass passage 11 installed on a throttle body 1 to the side of the surge tank 20 and forming a chamber 21 for temporary storage of the suction air connected to the by-pass passage on an outer shell of the surge tank 20.