UNINTERRUPTIBLE POWER SUPPLY DEVICE

Provided is an uninterruptible power supply device capable of responding to a variety of system abnormalities other than frequency fluctuation and voltage drop including instantaneous voltage drop. An uninterruptible power supply device 100 that is provided between a commercial power system 10 and an essential load 30 and that supplies AC power to the essential load 30, wherein the uninterruptible power supply device 100 is provided with: a power supply unit 2 that has an energy storage device 21 and is connected to a power line L1 for supplying power from the commercial power system 10 to the essential load 30; an open switch 3 for opening/closing the power supply line L1, the open switch 3 being provided on the power line L1 on the commercial-power-system side of the power supply unit 2; a system abnormality detection unit 5 for detecting a system abnormality, which is at least one of voltage rise, phase fluctuation, voltage imbalance, harmonic abnormality, and flicker, in addition to at least one of frequency fluctuation and voltage drop including instantaneous voltage drop, the system abnormality occurring on the commercial-power-system side of the open switch 3; and a control unit 6 that, when the detected system abnormality is equal to or greater than the tolerance of the essential load 30 or the power supply unit 2 against system abnormalities, opens the open switch 3 and supplies AC power from the power supply unit 2 to the essential load 30.