A data relay device includes a plurality of transmission ports that constitutes a logical port, and stores therein a MAC learning table and a CoS distribution table. The data relay device reads a MAC address and a CoS value from a frame, and reads a logical-port ID corresponding to the MAC address from the MAC learning table. The data relay device reads a transmission-port ID corresponding to the logical-port ID and the CoS value from the CoS distribution table, and outputs the frame to a transmission port indicated by the transmission-port ID. On the transmission port, the frame is stored in a transmission queue corresponding to the CoS value, and the frame is transmitted at a shaping rate assigned to the transmission queue.