An on-board communication system includes an on-board communication device and on-board devices. Each of the on-board devices includes a communication device controller configured to control data communication performed between the on-board communication device and a server and a priority setting portion configured to set priority ranks of the on-board devices for controlling the on-board communication device. When each of the on-board devices performs data communication with the server and if any one of the on-board devices is set to a higher priority rank, the on-board device is configured to transmit communication data to the on-board device that is set to a higher priority rank to perform data communication with the server via the on-board device that is set to a higher priority rank and the on-board communication device.