UNINTERRUPTABLE POWER SUPPLY DEVICE

Provided is an uninterruptable power supply device. An uninterruptable power supply device , which is provided between a commercial power system and an essential load and which provides AC power to the essential load , wherein the uninterruptable power supply device is provided with: a power supply unit , which has a power converter and a storage battery and which is connected to a power line L; an open switch for opening the power supply line L; a system abnormality detection unit 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; and a control unit which, opens the open switch and supplies AC power to the essential load