Disclosed herein is a variable venturi carburetor including at least one pressure controlling port provided at the lower peripheral portion of the suction piston and adapted to face to a mixing chamber defined directly downstream of the venturi portion. The pressure controlling port is located at such a position as to communicate with the suction chamber and an atmospheric pressure chamber during middle and high intake air flowing stages as the suction piston reciprocates transversely with respect to the venturi portion, and to communicate with the suction chamber and the mixing chamber during low intake air flowing stage.