An engine control apparatus which can ensure and maintain a stability and constant exhaust emission characteristics even in such a condition that a nature of a fuel used as present is unsure, and which is robust among different fuel natures, comprising a plurality of different nature fuel quantity computing means and an operating condition detecting means for detecting an operating condition of an engine, wherein a first nature fuel quantity computing means among the plurality of different nature fuel quantity computing means is used as a fuel quantity computing means during an engine start, and the fist nature fuel quantity computing means is forcibly changed over into a second nature fuel quantity computing means if an engine operating condition detected by the operating condition detecting means satisfies a predetermined term.