A repeater receiving an original frame from a connected Electronic Control Unit (ECU) by a normal port divides data stored in a data area of the received frame, and each of a plurality of divided data pieces is stored in the data area in each of a plurality of division frames to be sent out to a destination. Each of the plurality of division frames of the original frame is distributed to one of two ring ports according to a determination of the repeater, and each of the division frames is sent out therefrom to the destination. In such manner, the frame transmission time required for a transmission of the frame is reduced.