PURPOSE: To improve fuel measuring accuracy, and suppress temporal change by fitting a needle jet into a through-hole formed on a support boss of a sliding valve of an evaporator, and by fitting a jet needle having a measuring part thereto.

CONSTITUTION: A through-hole 31 is formed on a support boss 30 of a sliding valve 9 elevated through a diaphragm 13 according to the pressure inside a pressure receiving chamber 11, which hole 31 has one end opened to an upper end surface 30a of the support boss 30, and the other end opened to a lower bottom portion 9A. A needle jet 36 is fitted into the hole 31, which needle jet 36 is composed of a fuel measuring part 37 provided with a fuel measuring hole 39, a guide part 38 provided with a guide hole 40 having larger diameter than that of the fuel measuring hole 39, and a fuel injection hole 41 formed on the guide hole. A jet needle 32 is fitted into the needle jet 36, which jet needle 32 has a guide lever 33 fitted into the guide hole 40, and a measuring part 34 inserted into the fuel measuring hole 39. The measuring part 34 of the jet needle 32 is arranged while being centering-supported inside the fuel measuring hole 39.