a square waveform a plurality of transmission sections 4 as shown in fig1 are disposed at each of the locations 1 1 to 5 6 of fig2 both the transmission source and the many satellite sections comprises a transmission section as shown in fig1 the transmission section of fig 1 can transmit an output which can be received by its adjacent four side transmission sections the total system of fig2 comrises a transformer 1 for transferring 3 phase 6600 volt to single phase and 3 line 100 volt a main breaker 2 sub breakers 3 fig3 shows a block diagram of the controller 21 the controller 21 comprises a control circuit cnt 23 a cpu 24 a rom 25 a ram 26 and an i o line circuit 27 the cnt 23 receives data from a mate transmission section a self address switch and a mate address switch are connected to the controller 21 the self address switch is operated to set a self address of a transmission section the mate address switch is operated to set an address of a following mate transmission section to which data is transmitted from the transmission section the cpu 24 of fig3 detects the data from a previous mate transmission section the received data is stored in the ram 26 and further transmitted to the following mate transmission section therefrom the ram 26 contains a relay station counter for counting the number of relaying steps for the data to detect whether the number of relaying steps for the data equals a predetermined number set in this counter the number of relaying steps of the data in this counter is increased by the cpu 24 when one of the transmission sections receives and forwards the data.