An engine control apparatus which may be employed in automotive vehicles. The engine control apparatus is equipped with at least one of a combustion parameter or a controlled variable arithmetic expression. The combustion parameter arithmetic expression defines combustion conditions of the engine needed to achieve required values of engine output-related values such as exhaust emissions. The controlled variable arithmetic expression defines how to operate actuators for an operation of the engine to meet desired combustion conditions of the engine. The use of the combustion parameter or controlled variable arithmetic expression achieves simultaneous agreement of the engine output-related values with required values without mutual interference between combustion parameters associated with the combustion conditions.