POWER SUPPLY SYSTEM AND ELECTRICITY STORAGE DEVICE

When DC power to be supplied from a main power supply device drops and a voltage to be input to a load falls below a predetermined threshold value, a microcomputer controls a switch unit so as to start an ON-operation for supplying the DC power from a sub power supply device to the load, and when the DC power to be supplied from the main power supply device recovers, the microcomputer controls the switch unit so as to start an OFF-operation for restricting the DC power to be supplied from the sub power supply device to the load, restrict supply of the DC power from the sub power supply device to the load so that a voltage to be input to the load does not fall below a predetermined threshold value until a predetermined time has elapsed since start of the OFF-operation, and set supply of the DC power from the sub power supply device to the load to zero after the predetermined time has elapsed.