To provide an emergency power supply device that is inexpensive and has a long battery life.

In normal operation, a commercial power supply 10 is supplied to a load 9 and at the same time a battery 5 is charged. Immediately after power failure, power from the battery 5 is converted to an AC power by an inverter 6, the AC power is supplied to the load 9, and at the same time a cell motor is rotated and a high-frequency (400 Hz) generator 11 is operated. Then, when certain amount of time passes and an output voltage from the generator 11 becomes stable, an AC power from the generator 11 is supplied to a rectification circuit 11 as a DC power, and the DC power is converted to an AC power by an inverter 6, and the AC power is supplied to the load 9 via an UPS switch 8.