A vehicle electric power supply system includes: an electric power generating source; a battery; a first voltage converter configured to raise a voltage of the electric power generating source; a second voltage converter configured to raise a voltage of the battery; and an electric power converter configured to supply voltages, which are obtained by conversions by the respective first and second voltage converters, to a vehicle load. A power control unit, which includes the first voltage converter, the second voltage converter and the electric power converter, and the battery are integrated into a unitary component, and are placed in a front portion of a vehicle while isolated from a vehicle interior. Accordingly, it is possible to widen the vehicle interior and a luggage containing space in the vehicle's rear portion, and to avoid increase in the weight of the vehicle.