When three phase AC voltages (Vi1 to Vi3) from a commercial AC power supply (51) become abnormal, a control circuit (6) of an uninterruptible power supply device provides an OFF command signal to first to third switches (1a to 1c), and causes first to third power converters (2a to 2c) to output first to third direct currents, respectively, and quickly extinguish arcs in the first to third switches (1a to 1c). On this occasion, polarities of the first to third direct currents are the same as polarities of currents (Is1 to Is3) flowing into the first to third switches (1a to 1c), respectively, and the sum of values of the first to third direct currents is 0.