An air valve type carburetor comprises a pressure transducer provided for detecting pressure in the venturi portion of the carburetor and putting out electric signals corresponding to the pressure, a passage for introducing vacuum from a suction passage for supplying air-fuel mixture into an engine downstream of a throttle valve provided in the suction passage into a suction chamber containing slidably one end of a suction piston the other end of which is disposed in the suction passage for providing the venturi portion, an electromagnetic valve provided on the passage, and a control unit. The control unit receives electrical signals from the pressure transducer, compares the electric signals with a reference valve and put out electric signals corresponding to the difference. The electromagnetic valve controls vacuum induced into the suction chamber through the passage according to signals from the control unit so that the pressure in the venturi portion will be constant.