A PLC communication system includes a PLC; a plurality of devices; three or more communication processing nodes that are provided respectively in the PLC and the devices to allow the PLC to communicate with each of the devices; and a plurality of communication lines that connect the communication processing nodes to each other to allow data communication. The PLC detects an incommunicable state between two of the communication processing nodes. The PLC communication system further includes a display device, and in a case where there are a plurality of types of incommunicable states detected by the PLC, the display device displays a portion where communication lines constituting the incommunicable states among the plurality of communication lines overlap with each other, as a line failure portion.