Packet transmission method and packet transmission device

A packet transfer method in a network apparatus that transfers packets is disclosed. In the packet transfer method, a sending side apparatus generates two copies of a send packet, provides a sequence number identifying the same sending sequence to each of the copied packets, provides an identifier corresponding to a send/receive pair to each of the copied packets to send the packets, and a receiving side apparatus receives each of the packets with two receiving units; recognizes the identifiers each corresponding to a send/receive pair; identifies packets having the same information and the sequence based on the sequence number when the identifiers are the same; selects one of the packets of the same sequence so as to send the packet downstream, and discards another packet, wherein, when only one of the packets of the same sequence arrives, the arriving packet is sent downstream.