A control apparatus which is capable of ensuring both high-level stability and accuracy of control, even when controlling a controlled object having extremal characteristics or a controlled object a controlled object model of which cannot be represented. The control apparatus 1 includes a cooperative controller 30, an onboard model analyzer 40, and a model corrector 60. The model corrector 60 calculates the model correction parameter matrix θ, so as to correct the controlled object model defining the relationship between the intake opening angle θlin and the exhaust reopening angle θrbl and the indicated mean effective pressure Pmi. The onboard model analyzer 40 calculates first and second response indices RI1 and RI2 representative of correlations between θlin, θrbl, and Pmi, based on the controlled object model corrected using θ. The cooperative controller 30 calculates the θlin and θrbl such that Pmi is caused to converge to a target value Pmi_cmd, and determines an increasing/decreasing rate and increasing/decreasing direction of θlin and θrbl according to RI1 and RI2.