In a turbocharged internal combustion engine, an amount of cylinder suction air is calculated with sufficiently high accuracy to suitably control the internal combustion engine in consideration of influences of an exhaust pressure on a volumetric efficiency equivalent value without requiring a huge memory capacity, in fewer adaptive man hours, and under a low operation load. A correction calculation parameter is calculated using an exhaust pressure, an exhaust pressure for pre-correction volumetric efficiency equivalent value, and an intake manifold pressure, and a post-corrected volumetric efficiency equivalent value is calculated by correcting a pre-correction volumetric efficiency equivalent value using the correction calculation parameter. An amount of air entering a cylinder from an intake manifold is calculated on the basis of the post-correction volumetric efficiency equivalent value.