Abstract: There is provided a power supply system which is capable of eliminating inconvenience affecting a storage device in the event of a power failure. Monitoring control means monitors supply voltage provided by a DC power supply connected to a power-supplied device and outputs a warning signal to transition means when the absolute value of the supply voltage becomes equal to or smaller than a predetermined voltage value. The transition means causes transition of the operative state of a storage device included in the power-supplied device to an operation terminated state. More specifically, if the storage device is a hard disk drive and the hard disk drive is performing write operation, the hard disk drive is caused to undergo operative state transition to a stable state in which the write operation has been terminated.