A backup power-supply system according to the present invention includes a detector, a power storage unit, and a controller. The detector is configured to detect an abnormality of a power supply that supplies electric power to loads. The power storage unit is configured to supply electric power to the loads when the detector detects the abnormality of the power supply. The controller is configured to monitor a remaining electric energy remaining in the power storage unit, and impose, when the remaining electric energy of the power storage unit is smaller than a threshold electric energy, a limitation on the loads to which the power storage unit supplies the electric power.