PURPOSE: To reduce the load of a unit device at an originator side, by providing a register which stores the address information of each unit device, a storage device which stores the information given from a prescribed unit device and a device which transmits the stored information after designating an address respectively at a broadcast transmitting part.

CONSTITUTION: A unit device at the originator side transmits the data and its quantity to a broadcast transmitting part 4 and stores them to a storage device of the part 4. Then the data is delivered together with the stored address. The transmission line of the part 4 applies a loop type line, and each shift register is cascaded. Under such conditions, the output data and address are fed to the shift register of the unit device that is first connected. If the address of the unit device is coincident with either one of those designated addresses, the data in the shift register is latched to a memory in the unit device. Then the contents of the shift register are shifted and delivered to a transmission line to be supplied to the shift register of a unit device which is connected next. In such a way, the transmitted data is sent to a prescribed unit device.