Uninterruptible power supply

An uninterruptible power supply (10) of the present invention is provided with a battery (11); a DC-DC converter circuit (12) for regulating the voltage of the power delivered by the battery (11); and a voltage control circuit (13) for controlling the DC-DC converter circuit (12), so that the output voltage of the DC-DC converter circuit (12) is maintained at a standby voltage lower than a rated voltage under the condition of a power failure detection signal being not output from an external power supply and the output voltage of the DC-DC converter circuit (12) equals the rated voltage under the condition of the power failure detection signal being output from the external power supply.