A communication apparatus communicating with a plurality of another communication apparatuses through a network, includes a processor; and a communication device, in which the communication apparatus and the plurality of the other communication apparatuses are separated for each synchronous system, the processor generates a first time slot including a plurality of slots for communicating a synchronous message used in a first synchronous system, and generates a second time slot including a plurality of slots for communicating a synchronous message used in a second synchronous system, and the communication device transmits the synchronous message in a multicast manner in a first slot of the first time slot in the first synchronous system, and transmits the synchronous message in the multicast manner in a second slot different from the first slot of the second time slot in the second synchronous system.