UNINTERRUPTIBLE POWER SUPPLY DEVICE

PROBLEM TO BE SOLVED: To provide an interruptible power supply device capable of automatically and exactly switching a feeding condition without ceasing feeding to a load, improving safety and reliability and widely lightening a burden to maintenance workers. SOLUTION: The device comprises feeding circuits 5, 10 that conduct feeding to a load, notwithstanding an interruption of service of a commercial AC power 30, and an emergency bypass circuit 12 that is connected in parallel with the feeding circuits 5, 10, and mounts each of switch contacts 51, 52, 53, 54, 55 and 56 at the feeding circuits 5, 10 and the emergence bypass circuit 12 respectively. The conditions of the feeding circuits 5, 10 and the emergency bypass circuit 12 are monitored and, based on the result of the monitoring, each of the switch contacts is so controlled as not to cease the feeding to an AC load 40. By this control, the feeding is switched to and from the feeding circuits 5, 10 and the emergency bypass circuit 12.