Abstract: A plurality of slave stations receive a plurality of apparatus information signals concerning apparatus to be controlled (or sensors), and a master station allots the apparatus information signals to time slots in a transmission path and receives a specified apparatus information signal with priority from the respective slave stations. A priority change information signal adder in the master station adds a priority change information signal for changing priority of the information signals transmitted from each slave station to an information transmission signal string containing a sync signal and various information signals transmitted to each slave station. A multi-element information signal separator/processor in the master station separates and processes the multi-element information signals transmitted from each slave station, on the basis of the priority change information signal.