A cylinder intake air amount calculating apparatus for an internal combustion engine for calculating a cylinder intake air amount (GAIRCYLN) which is an amount of fresh air sucked into a cylinder of said engine, said cylinder intake air amount calculating apparatus comprising: intake air flow rate obtaining means for obtaining an intake air flow rate which is a flow rate (GAIR) of fresh air passing through an intake air passage of said engine; intake pressure detecting means for detecting an intake pressure of said engine; intake air temperature detecting means for detecting an intake air temperature which is a temperature of air sucked into said engine; theoretical cylinder intake air amount calculating means for calculating a theoretical cylinder intake air amount (GAIRSTD) based on the intake pressure and the intake air temperature; volumetric efficiency calculating means for calculating a volumetric efficiency (ηv) of said engine by dividing a preceding calculated value (GAIRCYLN(k-1)) of the cylinder intake air amount by the theoretical cylinder intake air amount (GAIRSTD); and cylinder intake air amount calculating means for calculating the cylinder intake air amount (GAIRCYLN) using the volumetric efficiency (ηv), the intake air flow rate (GAIR), and the preceding calculated value (GAIRCYLN(k-1)) of the cylinder intake air amount, wherein said volumetric efficiency calculating means updates the volumetric efficiency (ηv) more than once in one stroke period using the cylinder intake air amount calculated by said cylinder intake air amount calculating means as the preceding calculated value (GAIRCYLN(k-1), and said cylinder intake air amount calculating means updates the cylinder intake air amount (GAIRCYLN) more than once in one stroke period using the updated volumetric efficiency (η(vi)). intake air flow rate obtaining means for obtaining an intake air flow rate which is a flow rate (GAIR) of fresh air passing through an intake air passage of said engine; intake pressure detecting means for detecting an intake pressure of said engine; intake air temperature detecting means for detecting an intake air temperature which is a temperature of air sucked into said engine; theoretical cylinder intake air amount calculating means for calculating a theoretical cylinder intake air amount (GAIRSTD) based on the intake pressure and the intake air temperature; volumetric efficiency calculating means for calculating a volumetric efficiency (ηv) of said engine by dividing a preceding calculated value (GAIRCYLN(k-1)) of the cylinder intake air amount by the theoretical cylinder intake air amount (GAIRSTD); and cylinder intake air amount calculating means for calculating the cylinder intake air amount (GAIRCYLN) using the volumetric efficiency (ηv), the intake air flow rate (GAIR), and the preceding calculated value (GAIRCYLN(k-1)) of the cylinder intake air amount, wherein said volumetric efficiency calculating means updates the volumetric efficiency (ηv) more than once in one stroke period using the cylinder intake air amount calculated by said cylinder intake air amount calculating means as the preceding calculated value (GAIRCYLN(k-1), and said cylinder intake air amount calculating means updates the cylinder intake air amount (GAIRCYLN) more than once in one stroke period using the updated volumetric efficiency (η(vi)).