PURPOSE: To provide a PBX set data backup device capable of easily and effectively backing up set data without depending on a maintenance specialist.

CONSTITUTION: This device is provided with a storage device 106 whose stored contents are not eliminated even at the time of turning a power source OFF, a data processing function part for performing a prescribed processing to data inputted from a PBX 101 and outputting a processing result to the PBX 101, a backup function part 109 for backing up the set data of the PBX to the storage device and a switching function part for performing changeover between a data processing mode in which the data processing function part is operated and a backup mode in which the backup function part is operated corresponding to key operations and a case when the arrival of a set date and time is detected by a timer 112.