A communication system comprises a communication history table for recording as a communication history the communication cycles to transmit and receive a message by the broadcast communication, a communication cumulative value comparison unit for comparing the communication cumulative value stored into the communication history table with the communication cumulative value added to the received message, and a retransmission processing unit for deciding whether a communication apparatus receiving the message or a communication apparatus transmitting the message incurs an error and, for specifying a message to be retransmitted corresponding to the message missing when the transmitting communication apparatus incurs a message error.