To simplify the working to reduce the manufacturing cost by fitting a synthetic resin-made guide cylinder for guiding a piston valve to a cylindrical part crossing the intake passage of an aluminum-made body, and rounding the lower edge of the inside surface of the guide cylinder.

A piston valve 13 is supported by a vertical cylindrical wall 9 orthogonal to the intake passage 24 of an aluminum-made body 10 in such a manner as to be capable of rising and falling, and a fuel control needle valve 23 protruded down from the piston valve 13 is inserted to a fuel nozzle 22. The inside edge 5b of a membrane 5 is nipped by a vertical pair of presser plates 6, 8 in the upper end part of the piston valve 13, and a reverse cup-like support 16 for supporting the fuel control needle valve 23 is mounted within the piston valve 13 by engagingly locking a protruding piece 16a to an annular groove 15. In order to smoothly guide the rise and fall of the piston valve 13, a synthetic resin-made guide cylinder 14 rounded in the lower edge of the inside surface is fitted to the cylindrical part 9 of the body 10 to provide a required performance.