An in-vehicle communication system includes a plurality of nodes each connected to a first bus and a second bus. The first bus and the second bus each transmits a message with a priority according to the priority. Each of the plurality of nodes is configured to count the number of times that the message is transmitted from an own node to the first bus having lower priority than the message from other node; determine if the number of times of transmission exceeds a predetermined number of times; and transmit the message with the priority to the first bus or the second bus according to the determination.