PURPOSE: To obtain a fuel measuring device which shows high fuel measuring accuracy by means of a jet needle and a needle jet, and shows little temporal deterioration resulting in excellent durability.

CONSTITUTION: A jet needle 30 installed on a sliding valve 7 is inserted into a needle jet 16. The jet needle 30 has a cylindrical and columnar shape, while a controlling groove 31 is continuously formed from a rear end of a leading end of an outer peripheral surface 30A of the jet needle 30. The controlling groove 31 opened to the outer peripheral surface 30A has a constant width. Its depth is large at the leading end and small at the rear end.