To solve the problems of a meshing risk of a piston valve and a valve guide possessed by a conventional valve guide, and a sense of incongruity by inconsistency between an expected value of a driver and an actual output change for adjusting output of an internal combustion engine when a lower end part of the piston valve passes through on the valve guide, by an economical means, in a piston valve type carburetor having the valve guide for supporting the piston valve.

The substantially plate-like valve guide of crossing an intake passage downstream of the piston valve, is formed not in a conventional horizontal linear shape or an arch shape, but in a shape of being simply inclined to the other connection part from one connection part with a wall surface of the intake passage. Geometric meshing of the piston valve and the valve guide is avoided by imparting this simple inclination, and an invalid opening width intercepted by the valve guide inevitably generated when the lower end part of the piston valve passes through on the valve guide is also reduced, and the sense of incongruity is eliminated by restraining a sudden change in a valve opening area change rate.