VEHICLE POWER SUPPLY SYSTEM

In a vehicle power supply system (1), when a main power supply device (10) is normal, a backup controller (27) turns on a switch circuit (SW1) and turns off a switch circuit (SW2) to supply power from the main power supply device (10) to a load unit LD1 and a load unit (LD2), and can travel a vehicle in a normal mode which is in a normal driving state. On the other hand, when the main power supply device (10) is abnormal, the backup controller (27) supplies power from the backup battery (23) to the load unit (LD2) and does not supply power from the backup battery (23) to the load unit (LD1) by turning on the switch circuit (SW2) and turning off the switch circuit (SW1), and can travel the vehicle in the limit mode in which the functions are more limited than in the normal mode.