To obtain a power line carrier communication system employing a multiple power lines where transmitters connected between optional power line pairs can make communication without a bypass circuit.

A power line pair connected to slave station units 11a, 11b is detected and a RAM 7 and an EEPROM 9 store the detected power line pair. For power line carrier communication, a CPU 4 reads from the RAM 7 information on the slave station units 11a, 11b and information on the power line pair to which the slave station units 11a, 11b are connected, switches a changeover means 6 and allows a communication control means 5 to superimpose a communication signal on a commercial frequency signal and transmits the resulting signal.