PURPOSE: To provide a variable venturi type carburetor that is able to improve the extent of responsiveness to a fuel supply to a venturi part in time of sudden valve opening of a throttle valve as well as to check an increase of flow resistance in an intake passage due to the projection of a suction piston in time of sudden valve closing of the throttle valve, and besides, even if inertia force works on this suction piston, any possible variation in the piston is restrained, stabilizing the rotation of an engine in this way.

CONSTITUTION: This carburetor is so featured that a bypass path 25 is installed in the space between an intake passage 12b being situated at the more downstream side than a suction piston 15 and at the more upstream side than a throttle valve 24 and a suction chamber 21, and a check valve 27, preventing any backflow of air from the intake passage 12b side to the suction chamber 21 side, is installed in this bypass path 25.