PURPOSE: To simplify the constitution of a status reading processing at a master station, by a response of each slave station with a delay inherent to each device to a status batch reading command from a master data transferring station and making the addition of a slave station to a transmission line easy.

CONSTITUTION: A data transmission system is formed with a master station data transmitter 1 controlling data transmission on transmission lines 51, 52 and a plurality of slave station data transmitters 2∼4 connected to the transmission lines 51, 52. The slave station address batch command from the device 1 of this system is received at a reception circuit 21, a comparison circuit 22 discriminates whether the data is a status reading command, and the output is applied to a clock circuit 23. Discriminating information from a device discrimination information storing section 24 and a circuit 25 specifying a device discriminating information is applied to a comparison circuit 26. Whether or not the time counted at the circuit 23 is equal to the discriminating information of the specific time from the circuit 25 is discriminated at the circuit 26, a control circuit 27 is controlled and the data responds to the transmitter 1 with a specific delay in the devices 2∼4.