In a data communication system which has a common transmission line, a plurality of transceivers connected to the transmission line and data processors connected to the respective transceivers, and in which data from the data processor is delivered to the common transmission line through the corresponding transceiver, and data from the common transmission line is delivered to the data processor through the transceiver, so as to perform data communications among the data processors; a data communication system wherein said each transceiver comprises a first circuit which checks if an address of the data received from the transmission line has been received without any transmission error, a second circuit which checks if the address is one directed to the particular transceiver when the absence of the transmission error has been decided by the first circuit, a third circuit which turns back and delivers the received data when the address directed to the particular transceiver has been decided by the second circuit, and a fourth circuit which compares the sent data with the data turned back from another transceiver, the sending of the data being stopped when disagreement has been detected by the fourth circuit.