The transmission side adds retransmission identification information to the RLC sub-PDUs obtained by dividing an RLC PDU, and transmits the RLC sub-PDU with the retransmission identification information added thereto. The reception side refers to the retransmission identification information added to the received RLC sub-PDUs, and stores only the RLC sub-PDUs having retransmission information the same as an assumed value which is preset, into a buffer, and assembles an RLC PDU using the RLC sub-PDUs having the same retransmission identification information.