To guide air in an intake passage to a main fuel nozzle only in a high-speed operation region of an engine and to supply fuel-air mixture from a fuel injection hole of the main fuel nozzle.

A part between a fuel jet 59 of the main fuel nozzle 56 and the fuel injection hole 56a is connected to the inlet of the intake passage 16 through air passages 74 and 71. A vibration ball valve B that opens when engine speed exceeds a predetermined value and an air jet 69 are disposed in series in the air passages 74 and 71. Fuel flow rate is set to the optimum value required by the engine to improve transition performance such as acceleration of the engine and prevent degradation of exhaust gas.