An in-vehicle communication system includes a master control unit mounted on a vehicle, a plurality of slave devices mounted on the vehicle, a plurality of buckles provided in association with each of a plurality of seats mounted on the vehicle, and at least one switch unit configured to generate a signal in accordance with an attachment and detachment state of at least one of the plurality of buckles. The master control unit is communicably connected to each of the slave devices. The master control unit controls the plurality of slave devices based on the signal generated by the at least one switch unit.