To perform appropriate adjusting with less revolution number of a regulating valve in an adjusting device for adjusting a fuel flow rate by inserting a needle-type valve element of the regulating valve into a throttle hole of a fuel passage.

A compensation passage 16 having a measuring jet 17 for supplying an engine minimum request flow rate is arranged to the valve element 13 of the manual regulating valve 12 inserted into the throttle hole 18 of a main fuel passage 7. The flow rate between a flow rate supplied from the compensation passage 16 at a gap between an outside peripheral surface 13a of the valve element 13 and an inlet edge 18a of the throttle hole 18 and an engine request maximum flow rate is adjusted. Accordingly, fuel adjustment is performed with the less revolution number of the regulating valve 12, and an accurate fine adjusting is realized with the less revolution number by reducing a cone angle of a circular cone part 13A for the fine adjusting.