In an apparatus for controlling an engine, as an air flow sensor for measuring intake air flow quantity, a heater resistor having temperature-resistance characteristic and a temperature sensitive resistor for sensing air temperature are provided in an intake passage, and heating electric power is supplied to the heater resistor in response to a start signal generated periodically. The heating electric power is cut off when the temperature of the heater resistor is raised to a specified reference temperature predetermined in accordance with the air temperature, so that an output signal indicative of the time width in which the heating electric power is supplied is applied to an electronic control unit to measure air flow quantity therefrom. Further, compensation coefficient stored in a memory is derived in correspondence to the intake air temperature sensed by the temperature sensitive resistor, and the output signal is compensated for by the compensation coefficient to compensate the measured air flow quantity. Based on the compensated air flow quantity, fuel injection quantity, ignition timing or the like is computed in the electronic control unit.