PURPOSE: To obtain an uninterruptible power-supply device which continues supplying power to a load from a power-supply battery in the case of the service interruption of a commerical power supply and in which the time during which the power supply can be supplied to the load from the battery in the case of the service interruption can be checked by a simple operation.

CONSTITUTION: An uninterruptible power-supply device is provided with a battery charging means 1 which uses a commercial power supply as an input, with a battery 2 which is connected to the battery charging means 1, with an inverter 3 which uses the battery 2 as an input and which outputs an AC power supply, with a changeover means 4 which is connected to the commercial power supply, to the inverter 3 and to a load, with a detection switch 5, with a battery-voltage detection means 6, with a backup-time display means 7 and with a microcomputer 8 which processes and controls them.