A power line communications system includes slave apparatuses individually connected to multiple electric power line wirings; a master apparatus connected to one of the multiple electric power line wirings; and couplers each connected between the master apparatus and the others of the multiple electric power line wirings. The master apparatus includes a communicator for performing power line communications with the slave apparatuses via the electric power lines; a power supply terminal device connected to the one electric power line wiring; a communication connector provided between the communicator and the power supply terminal device; and a coupler connecting terminal device connected to each of the couplers via a signal line. The communication connector has a first capacitor connected to the power supply terminal device for cutting off a frequency component of commercial power supply and transmitting a frequency component for use in the power line communications, and a first transformer connected between the first capacitor and the communicator. The coupler connecting terminal device is connected between the first capacitor and the first transformer.