Abstract: An engine control apparatus comprises a throttle sensor, a pressure sensor for detecting a pressure in the intake manifold of an engine as a value of the absolute pressure, an engine revolution speed detector, a zone detector for detecting the fact that a signal value indicating a degree of opening of a throttle valve and a signal value indicating an engine revolution speed fall in a predetermined atmospheric pressure detection zone and a processing unit to calculate a value of atmospheric pressure by adding a set value to a signal of pressure upon detecting said values being in the detection zone. A timer may be provided to detect the fact that the signal values of the degree of opening of the throttle valve and the engine revolution speed are continuously in the atmospheric pressure detection zone for a predetermined time.