A control device for an internal combustion engine. An object of the present invention is to provide a control device for an international combustion engine for highly accurate absolute pressure correction irrespective of the length of an adiabatic compression stroke period. When the number of cylinders in an engine is n (n is an integer of 2 or more), an adiabatic compression stroke period of one cylinder preceding another cylinder to be corrected into its absolute pressure by a 1/n cycle (ignition timing —IVC) is compared with a threshold CATH (step 100). In the step 100, the absolute pressure correction is carried out based on PVκ=constant when the adiabatic compression stroke period is longer than the threshold CATH (step 110). On the other hand, the absolute pressure correction is carried out based on a value PIP detected by an intake pipe pressure sensor when the adiabatic compression stroke period is shorter than the threshold CATH.