A control apparatus for use with an electric power conversion system which is equipped with a dc/ac converter connected to an electric rotating machine and a capacitor joined to input terminals of the dc/ac converter. The control apparatus stores an angle of rotation (i.e., start angle θ0) of the electric rotating machine before start of control of energization of the electric rotating machine to discharge the capacitor and determines command currents idr and iqr which will result in zero (0) torque in the electric rotating machine. The control apparatus includes a command current correcting circuit which corrects the command currents idr and iqr by a difference between a current angle θ of rotation of the electric rotating machine and the start angle θ0, thereby avoiding constant rotation of the electric rotating machine when the capacitor is discharged.