PURPOSE:To secure transmission of the telegram having the channel number added through the transmission line by giving other control information to the converter when the decoded telegram is identified as the relaying and then rewriting the channel number to transmit the information of the outgoing line and the telegram. CONSTITUTION:Node B receives the telegram from line 1 at receiver RCVR and then gives the received telegram with the incoming line number 1 added to decoder DECR. Thus, DECR draws out the control table of line 1, and an index is given to the table with the telegram channel number (a). Then the control information corresponding to the channel number is extracted and decoded. When the telegram is identified as the relaying, other control information is given to converter CONV, where the channel number is rewritten from (a) to (b) and the information of outgoing line 4 plus the telegram are transmitted via transmitter SNDR. In this way, the channel number correspondence is secured between the adjacent nodes, and the telegram with the channel number added can be transmitted via the transmission line.