The quality and performance of the connectionless communications system are improved. When a BOM is received, the destination address DA of the L3-PDU stored in the payload of the BOM is retrieved, and the tag information is obtained from the DA (S11). The output message identifier MID is reserved (S12), and the tag information and output MID are assigned to the BOM (S13). Then, the tag information and output MID are written to the table. When a COM is received, the tag information and output MID are retrieved using the MID of the COM as a key, and the information is provided for the COM (S31 and S32). When an EOM is received, the tag information and output MID are retrieved using the MID of the EOM as a key, and the information is provided for the EOM (S41 and S42). Then, the output MID is released (S43).