The control apparatus controls a controlled variable of the electric rotating machine by manipulating an output voltage of a power converter circuit including switching elements operated at a set modulation index to connect positive and negative terminals of a DC power source to corresponding terminals of the electric rotating machine. The control apparatus includes a prediction section configured to predict the controlled variable for each of a plurality of cases where the power converter circuit is set in a corresponding one of a plurality of predetermined operating states, a manipulation section configured to determine one of the predetermined operating states depending on a result of evaluation by an evaluation function, and set the converter circuit to the determined operating state, and a feedback control section configured to feedback-control the output voltage of the power converter circuit at a target value by manipulating the input parameters of the evaluation function.