An intake air pressure P1 and a target control value S1 under the condition that the internal combustion engine is in a steady operating state and the condition that the turbocharger has its supercharging efficiency set to a ratio according to the engine operating state are estimated based on engine parameters, and an intake air pressure P2 and a target control value S2 under the condition that the internal combustion engine is in the steady operating state and the condition without supercharging by the turbocharger are estimated based on the engine parameters. A target control value S0 associated with an actual intake air pressure P0 under the condition that the internal combustion engine is in a transient operating state is calculated by performing interpolation on the target control values S1, S2 based on a relation between the intake air pressures P1, P2 and the actual intake air pressure P0.