A vehicle electric power system comprising: a battery; a first DC-DC converter configured to step down a voltage of electric power supplied from the battery to supply a load with the converted electric power whose voltage is stepped down; a second DC-DC converter configured to step down the voltage of the electric power supplied from the battery; an electric power storage unit configured to accumulate energy of the electric power whose voltage is stepped down to a first voltage by the second DC-DC converter; and a control circuit configured to control the first DC-DC converter and the second DC-DC converter; an electric power receiving unit configured to receive electric power from an external device that is capable of supplying electric power, a voltage of the supplied electric power and the received electric power being less than the first voltage, wherein the control circuit is started with the electric power received by the electric power receiving unit and then controls the second DC-DC converter to step down the first voltage of the electric power of the electric power storage unit to the second voltage which is less than the first voltage such that the control circuit is operated with electric power from the second DC-DC converter, a first feeding path between the first DC-DC converter and the load; a second feeding path between the second DC-DC converter and the electric power storage unit; characterised in that the vehicle electric power system further comprising: a switching circuit configured to switch conductivity between the first feeding path and the second feeding path, wherein the switching circuit includes: a switch configured to turn on/off the conductivity between the first feeding path and the second feeding path; and a diode connected in parallel with the switch, whose anode is connected to the first feeding path and whose cathode is connected to the second feeding path, and that the control circuit controls the switching circuit to have a conduction state between the first feeding path and the second feeding path be conductive in response to detecting a lack of the electric power supplied from the first DC-DC converter to the load. a battery; a first DC-DC converter configured to step down a voltage of electric power supplied from the battery to supply a load with the converted electric power whose voltage is stepped down; a second DC-DC converter configured to step down the voltage of the electric power supplied from the battery; an electric power storage unit configured to accumulate energy of the electric power whose voltage is stepped down to a first voltage by the second DC-DC converter; and a control circuit configured to control the first DC-DC converter and the second DC-DC converter; an electric power receiving unit configured to receive electric power from an external device that is capable of supplying electric power, a voltage of the supplied electric power and the received electric power being less than the first voltage, wherein the control circuit is started with the electric power received by the electric power receiving unit and then controls the second DC-DC converter to step down the first voltage of the electric power of the electric power storage unit to the second voltage which is less than the first voltage such that the control circuit is operated with electric power from the second DC-DC converter, a first feeding path between the first DC-DC converter and the load; a second feeding path between the second DC-DC converter and the electric power storage unit; characterised in that the vehicle electric power system further comprising: a switching circuit configured to switch conductivity between the first feeding path and the second feeding path, wherein the switching circuit includes: a switch configured to turn on/off the conductivity between the first feeding path and the second feeding path; and a diode connected in parallel with the switch, whose anode is connected to the first feeding path and whose cathode is connected to the second feeding path, and that the control circuit controls the switching circuit to have a conduction state between the first feeding path and the second feeding path be conductive in response to detecting a lack of the electric power supplied from the first DC-DC converter to the load. a switching circuit configured to switch conductivity between the first feeding path and the second feeding path, wherein the switching circuit includes: a switch configured to turn on/off the conductivity between the first feeding path and the second feeding path; and a diode connected in parallel with the switch, whose anode is connected to the first feeding path and whose cathode is connected to the second feeding path, and that a switch configured to turn on/off the conductivity between the first feeding path and the second feeding path; and a diode connected in parallel with the switch, whose anode is connected to the first feeding path and whose cathode is connected to the second feeding path, and that the control circuit controls the switching circuit to have a conduction state between the first feeding path and the second feeding path be conductive in response to detecting a lack of the electric power supplied from the first DC-DC converter to the load.