A communication system, comprising: a transmission-side processing device is provided in a controller which controls a transport vehicle which transports an article, and a reception-side processing device provided in the transport vehicle, wherein the transmission-side processing device and the reception-side processing device communicate using a plurality of communication lines (1A, 1B), the transmission-side processing device concurrently transmits the same telegraphic messages as sets of data being described in accordance with a certain format via each of the plurality of communication lines (1A, 1B), the transmission-side processing device includes a priority determiner which determines a priority of a telegraphic message to be transmitted and transmits the telegraphic message either via the plurality of communication lines (1A, 1B) or via only one of the communication lines (1A, 1B) depending on the priority determined by the priority determiner, wherein the priority determiner determines that the priority is high if a telegraphic message contains an instruction which causes the transport vehicle to execute a predetermined operation, and determines that the priority is low if the telegraphic message does not contain the instruction, and the reception-side processing device is capable of concurrently receiving telegraphic messages via each of the plurality of communication lines (1A, 1B), and in a case where a same telegraphic message as a previously received telegraphic message is received later, invalidates said same telegraphic message while processing the previously received telegraphic message. a transmission-side processing device is provided in a controller which controls a transport vehicle which transports an article, and a reception-side processing device provided in the transport vehicle, wherein the transmission-side processing device and the reception-side processing device communicate using a plurality of communication lines (1A, 1B), the transmission-side processing device concurrently transmits the same telegraphic messages as sets of data being described in accordance with a certain format via each of the plurality of communication lines (1A, 1B), the transmission-side processing device includes a priority determiner which determines a priority of a telegraphic message to be transmitted and transmits the telegraphic message either via the plurality of communication lines (1A, 1B) or via only one of the communication lines (1A, 1B) depending on the priority determined by the priority determiner, wherein the priority determiner determines that the priority is high if a telegraphic message contains an instruction which causes the transport vehicle to execute a predetermined operation, and determines that the priority is low if the telegraphic message does not contain the instruction, and the reception-side processing device is capable of concurrently receiving telegraphic messages via each of the plurality of communication lines (1A, 1B), and in a case where a same telegraphic message as a previously received telegraphic message is received later, invalidates said same telegraphic message while processing the previously received telegraphic message.