An ECU in an electric power generation control system obtains a vehicle state containing a battery state and a driving state of a motor vehicle. The ECU calculates charging parameters necessary for maintaining a residual charge of a battery and vibration suppression parameters necessary for suppressing vibration of a vehicle. An exciting current setting section as a function of the ECU determines an exciting current flowing in an excitation winding of an alternator on the basis of the charging parameters and the vibration suppression parameters.