A communication device includes a plurality of controllers, a plurality of buses that transmit transmission information, and a gateway to which the plurality of buses are collectively connected. Each of the plurality of controllers has a pattern table that defines, for each piece of the transmission information, a transmission bus pattern, and controls the input and output of the transmission information according to the pattern table. Each of the plurality of controllers is connected to at least two buses, and outputs, to the gateway via all of the connected buses, check information for a confirmation of connections to the connected buses. The gateway determines an interrupted bus from which no check information is input, and outputs, to each of the plurality of controllers, a route switch instruction instructing use of a pattern table that does not include the interrupted bus(es).