The invention is to provide a relay signal system or a device which enables the use of signal related services such as IP phone services even if a supply of power from a commercial AC power source is stopped, for instance, due to a power outage. The signal relay device comprises: a power reception terminal that is coupled to an AC power source, a plurality of connectors containing a plurality of terminal pins for receiving and transmitting signals such as packet signals in which the terminal pins are coupled to each other by wire, and a power charging unit, which is coupled to the power reception terminal by wire and stores a backup power charged by an AC power provided from the power reception terminal by wire and supplies the backup power to wires coupled to a part or all of the plurality of connectors.