PURPOSE: To keep off any output variation caused by intake pulsation by controlling a high load condition where this intake pulsation grows larger, so as to make no compensation, in a device which compensates air flow meter output according to a variation in the air flow meter itself.

CONSTITUTION: This detector is provided with a calculating means 3 calculating a signal (for example, fundamental fuel pulse width Tp) equivalent to an air quantity per unit rotation from output of an air flow meter 2 generating the output conformed to the air quantity at the upstream of an inlet throttle valve. Then, a weighted means is added to the calculated result hereat by a weighted average means 4, and using a variation per unit time of this weighted mean value, the weighted mean value is preferentially compensated by a preferential compensation means 5. At this time, whether an engine is in a high load condition or not is judged by a high load judging means 6 from a load signal of the engine, and when the high load condition is the case, the weighted mean value is selected and when it is not, the preferential compensation value is selected to be selected each by a selector means 7, respectively, then this value after being selected is outputted as a signal equivalent to a cylinder air quantity.