An electric power supply system for a starter comprises a capacitor. This capacitor is charged by a battery through a charging circuit including resistors that charges the capacitor by dividing a voltage of the battery by the resistors. This capacitor is discharged to the starter through a discharge circuit that applies to the starter a charged voltage of the capacitor in addition to the voltage of the battery. When the starter is driven, the connection of the capacitor is switched from the charging circuit to the discharging circuit by an ECU and switching relays.