PURPOSE: To improve the transmission efficiency of the whole system by constituting plural data transmission devices connected to one transmission line annularly and the transmission line as a frequency dividing multiple system and circulating different tokens in respective frequencies.

CONSTITUTION: N data transmission devices 1 are connected annularly through one transmission cable 3 and data processors 2 for transferring information are connected to respective devices 1. A token from a receiving cable 1a is inputted to a reception control circuit 12 through channels CHs 111∼11n in a receiving interface IF circuit 11, and if the address in CHs does not coincide with the that of the office itself, the token is transmitted to a transmission cable 1b through the CHs 211∼21n in an transmission IF circuit 21. When the address of the CHs coincides with that of the office itself, free tokens in respective CHs are sent from the circuit 12 to the processor 2 through a receiving circuit 13 and an external IF circuit 31 to be processed. When information is to be sent from the processor 2, an address and transmission information are added to the free token and the information is sent as a busy token to the cable 1b through a transmission circuit 23 and the circuits 22, 21.