A vehicle-mounted video communication system is equipped with first to fourth image pickup devices, mounted on a vehicle, for transmitting video data obtained by picking up an image; first to fourth video processing devices for processing the video data; and a vehicle-mounted video relay device having connection sections connected to the first to fourth image pickup devices and the first to fourth video processing devices via communication cables and configured to transmit the video data transmitted from the first to fourth image pickup devices selectively or in a multiplexed state to the first to fourth video processing devices.