A control system for controlling an alternator driven by an engine, for generating electric power, has a changeover switch for selectively switching destination of electric power generated by the alternator to a plurality of electric loads having respective different load voltage values. An ECU controls switching operation of the changeover switch and controls the alternator electric power, according to a direction in which the changeover switch has been switched. The ECU detects voltage of the alternator electric power when the destination of the alternator electric power is to be switched from a first electric load having a higher load voltage value of the plurality of electric loads to a second electric load having a lower load voltage value of the same, and causes the changeover switch to switch the destination of the alternator electric power from the first electric load to the second electric load after it is determined that the voltage of the alternator electric power has been changed from a predetermined higher voltage value to a predetermined lower voltage value.