Cylinder intake-air quantity calculating apparatus and method for internal combustion engine

In apparatus and method for calculating a mass air quantity sucked into a cylinder of an internal combustion engine, income and outgo calculations between a mass air quantity flowing into an intake manifold and that flowing out from the intake manifold is performed to calculate the mass air quantity within the intake manifold and calculates a mass air quantity sucked into a corresponding cylinder of the engine on the basis of the mass air quantity within the intake manifold and a volume of the corresponding cylinder; and the mass air quantity within the intake manifold calculated as a result of the income and outgo calculations of the mass air quantity during a stop of the engine is corrected on the basis of a crank angular position during a step of the engine to calculate finally the mass air quantity within the intake manifold during the stop of the engine.