PURPOSE: To promote atomization of fuel throughout the whole area of the operation state of an engine and to provide ideal air-fuel mixture throughout the operation state of an engine by forming a notch in a needle jet, forming a groove in a pilot outlet, and forming a groove in a bypass.

CONSTITUTION: By forming a notch 1 in a cylindrical needle jet 4, atomization of fuel is promoted by also utilizing a velocity of flow of intake air flowing along the periphery of the needle jet 4. By forming grooves 2 and 3 in a pilot outlet 5 and a bypass 6, respectively, opened in a plane-form manner to the wall surface of a venturi part 9, fuel is easily guided through the opening parts of the pilot outlet 5 and the bypass 6 along the slopes of the grooves 2 and 3 even at a low negative pressure. This constitution promotes atomization of fuel throughout the whole area of the operation state of an engine, improves combustion efficiency, purifies exhaust gas, improves operability, reduces fuel consumption, and reduces the generation of noise.