Communication device and communication system capable of detecting a failure of a device connected to a communication bus

A communication system, comprising:

• a plurality of communication devices connected to a communication bus,
• wherein the plurality of communication devices transmit data through the communication bus according to an order set in advance when a beacon signal is transmitted,
• when there is no transmission data to be transmitted to one of remaining communication devices other than a target communication device included in the plurality of communication devices, the target communication device transmits dummy data whose transmission destination is different from the remaining communication devices,
• a communication device different from the target communication device among the plurality of communication devices includes a processing unit that performs processing, and
• the processing unit determines whether or not the target communication device has transmitted data at a timing at which the target communication device transmits data, and changes the order when it is determined that the target communication device has transmitted no data.