An in-vehicle communication system including independent communication hub devices each incorporating a function of relaying communication and a function of controlling a communication path among a plurality of communication connectors, in which each of the communication hub devices includes an internal power supply unit configured to generate, based on input power supply power supplied from a main power supply on a vehicle side, stabilized power supply power necessary for operation of an internal circuit, and a backup power supply output unit configured to supply the input power supply power or the stabilized power supply power generated by the internal power supply unit to the other communication hub device as backup power, in which a backup power supply line is provided which connects the backup power supply output units of the plurality of communication hub devices.