An air/fuel ratio compensating device is provided for association with an internal combustion engine having a fuel control valve, air suction pipe means and pedal accelerator means, the compensating device including an area flow metal system made up of a flow detection valve positioned upstream in the air suction pipe means and operatively associated with the fuel control valve, a flow control valve positioned downstream in the air suction pipe means in series with the flow detection valve and being operatively connected to the accelerator pedal means, the area flow meter system enabling the difference in pressure existing on opposite sides of the flow detection valve to be maintained at a predetermined value to insure that the amount of air flow is proportional to the opening area of the flow detection valve thus permitting a determination of the amount of air flow on the basis of the opened area of the flow detection valve, a feedback control mechanism for controlling the area control flow meter and including pressure sensitive amplifier means to detect and amplify the deviation of the difference in pressure, valve opening means connected to the amplifier means and operatively associated with the flow detecting valve for opening and closing the flow detection valve by the output from the amplifier means, and compensating means for compensating for the set value placed in the pressure sensitive amplifier means according to the operating conditions of the internal combustion engine.