To reduce a rate of fuel consumption increasing as an engine speed of an engine increases.

This carburetor is featured in that a spray nozzle 21 of fuel is arranged in a throat part 20a of a venturi tube 20, a fuel filling chamber 22 conducting to this spray nozzle 21 is arranged, a needle valve 24 for adjusting a flow quantity of fuel is arranged between a chamber 23 conducting to a fuel tank and the fuel filling chamber 24, a base end part 24a of this needle valve 24 is installed in one end part 25b of a lever 25 having an intermediate part 25a rotatably supported by a support shaft 25d, the other end part 25c of this lever 25 is allowed to abut to an abutting part 27a arranged in a central part of a surface of a diaphragm 27 arranged in a boundary between the fuel filling chamber 22 and a gas filling chamber 26, and a ventilating hole 28 conducting to the gas filling chamber 26 is arranged in the best design position of a diametrally contracted part 20b of the venturi tube 20 so that a rate of increasing in fuel consumption reduces more than a conventional carburetor as an engine speed of an engine having the carburetor increases.