EMERGENCY POWER SUPPLY DEVICE

PROBLEM TO BE SOLVED: To provide an emergency power supply device with reduced degradation of a capacitor.SOLUTION: An emergency power supply device 1, connected between commercial power 8 and a load 15, feeds power from the commercial power 8 to the load 15 in normal times, and feeds power from a capacitor to the load 15 in an emergency when the commercial power 8 drops instantaneously or fails. The emergency power supply device 1 comprises a capacitor control device 4 for controlling the charging and discharging of a capacitor 2. The capacitor control device performs control operation in a first mode, in normal time, where the voltage across the capacitor 2 is kept below a rated voltage, and responding to an emergency prediction signal, performs control operation in a second mode where the voltage across the capacitor 2 is kept at the rated voltage.