A relay connector unit for communicating an electronic control unit with a plurality of electronic devices includes: a first connecting unit connected to the electronic control unit; a second connecting unit having a plurality of circuits connected to the electronic devices respectively; and a transferring unit connected to the first connecting unit and the second connecting unit. The transferring unit transmits first information received by the first connecting unit from the electronic control unit to at least one of the electronic devices through a corresponding circuit, on the basis of circuit identifying data included in first information, the circuit identifying data indicating the corresponding circuit to be transferred to or from. The transferring unit appends the circuit identifying data to second information received from one of the electronic devices through the corresponding circuit to transmit the second information to the electronic control unit through the first connecting unit.