PURPOSE: To realize the transmission of the information about the carriers of the same frequency sent from several terminal units to the line concentrator by including the identification information of the terminal unit and the generation information of the terminal within the time of 1/4 minimum repetitive cycle and then carrying out the repetitive transmission during the transmission period.

CONSTITUTION: Antenna switch circuit 5 is operated with the equal time interval by the output of the communication control part of transmitters of terminal units S-1, S-2...S-N, thus securing intermittence between communication filter 4 and transmission antenna 6. In other words, the 1st terminal unit features repetitive cycle T and transmission time T/2, the 2nd terminal unit features repetitive cycle 2T and transmission time T, and thus in the same way final terminal unit S-N features repetitive cycle 2N-1×T and transmission time 2N-1×T/2, thus repeating the transmission and discontinuation of transmission. Line concentrator CL-1 receives correctly the information from each terminal unit within the time of 1/4 minimum repetitive cycle and within time 2N-1×T. In this way, the information can be transmitted to the line concentrator from several terminal units using carriers of the same frequency.