To reduce a sliding resistance of a negative pressure operated valve so as to improve the dynamic characteristic of the valve by injection molding tetrafluoroethylene-ethylene copolymer to form a piston ring fitted in a ring groove formed at an upper end of the negative pressure operated valve part.

This carburetor comprises a negative pressure operated valve part 11A supported to move freely in a negative pressure operated valve guiding cylinder opened upward from an intake path 2. At an upper portion of the part 11A, an annular portion 11B fitted to a negative pressure cylinder hole 9 is formed integrally, and a ring groove 11C is formed to be open outward in the portion 11B while a piston ring 12 is fitted thereto. This ring 12 is formed by injection molding tetrafluoroethylene-ethylene copolymer. With the constitution, a sliding resistance with the hole 9 can be reduced, and the profiling characteristic to the hole is improved to thereby ensure an accurate fuel control.