PURPOSE: To supply the idling fuel properly and stably by inserting an idling fuel jet and a spring into a hard passage part in order, and driving an idling air bleed jet or a plug.

CONSTITUTION: An idling fuel jet 12 and a spring 22 are inserted from the upper end of a hard passage part 8, and an idling air bleed jet 13 or a plug 23 is driven into the upper end to compress the spring 22, and the idling fuel jet 12 is pressed to down with a spring load of the spring 22 to be fixed under the condition that a seat part 21 thereof is adhered to a seat part 18 of the hard passage part 8. The fuel measured by the idling fuel jet 12 enters to a lateral passage part 10 through a space between coil of the spring 22 and flows to an idle port 16 and an idling port 17. Namely, chips to be caused by the screws is eliminated and while a passage resistance by a coil spring is constant in outline, and a cavity between the idling fuel jet 12 and in a seat part of the hard passage part 8 is eliminated.