A control device used for an internal combustion engine and capable of determining an actuator operation amount is provided. The control device includes a computation element that uses engine status amounts to compute the actuator operation amount. The computation element uses a model that includes a plurality of submodels arranged in a hierarchical sequence. The computation element computes the actuator operation amount by using a parameter calculated by the lowest level submodel and changes the number of higher-level submodels to be used in combination with the lowest level submodel in accordance with the operation status of the internal combustion engine.