In a packet transfer method, a packet to be transferred to a destination access network is generated and transmitted to a transmission-source packet transfer apparatus connected to the transmission-source access network. The packet is converted into a superpacket having a length n times (n is an integer of 2 or more) larger than a fixed-length cell as a switching unit of a relay apparatus arranged on a network serving as a backbone, and sent to the network. The superpacket is relayed using the relay apparatus and transferred to a destination packet transfer apparatus connected to the destination access network. The packet generated by the transmission-source access network is reassembled on the basis of the superpacket transferred from the network, and sent to the destination access network. A packet transfer apparatus and packet communication system are also disclosed.