Abstract: An in-vehicle communication system includes communication transmission paths, a first electronic device and second electronic devices each of which is connected directly/indirectly with the first electronic device through the communication transmission path(s), the first electronic device includes an evaluation unit sending a predetermined evaluation signal to the second electronic device(s) as target device(s), receiving a reply signal sent back by the target device in response to the evaluation signal, and evaluating a transmission quality of the communication transmission path(s), each of the second electronic devices includes a first communicator folding back a propagation direction of the evaluated signal received as the target device and sending the evaluated signal as the reply signal to the first electronic device, and the evaluation unit stores an evaluation result about the transmission quality, in association with the second electronic device that is the target device.