To optimize an operation parameter determined by a control device of an internal combustion engine.

An inclination of a road surface, on which a vehicle exists, is detected, and an engine rotation speed in fuel injection or ignition and the amount of intake air to be infilled into a cylinder are repeatedly presumed on the basis of the detected inclination of the road surface and the amount of change in the degree of opening of an accelerator. Thus, since the engine rotation speed and the amount of intake air, which become the basis for the determination of the operation parameter such as the amount of fuel consumption, are not greatly separated from the engine rotation speed and the amount of intake air when control is performed by actually using the operation parameter, the operation control of the internal combustion engine can be performed by using the optimum operation parameter.