PURPOSE: To obtain an efficient response system by transmitting collectively a data reception end confirming signal to all secondary stations controlled by a primary station.

CONSTITUTION: When a transmission request signal is incoming from the primary station A to the secondary stations B, C or the like, data is transmitted to the primary station A via a loop from the secondary stations B, C having data to be transmitted. The primary station A receiving the data from the secondary stations B, C... edits and forms a response message as the data reception end confirming signal which is objects of all the secondary stations and transmits the result to the secondary stations B, C.... A common station number taking the address to all the predetermined secondary stations is stored in a message transmission address N next to a start flag F of the response message in this case. A control information section H represents data content stored succeedingly and when TYP=1, it is represented that the data stored successively is response information and when TYP=0, it is represented that the succeeding data is data including an instruction or the like.