PURPOSE: To quicken the data transfer speed while keeping the access control speed low by constituting a loop transmission line as frames each composed of a control channel and a data transfer channel and making the band of the control channel smaller compared with the band of the data transfer channel.

CONSTITUTION: When a transmission request takes place in a node, a control circuit 28 connects a switch 25 from the loop side to a token transmission circuit 27 and switches a control loop 12 from the passing state into the reception state. Thus, when a token frame is inputted, it is fed to the control circuit 28 but not to a downstream node, when the reception of the token frame is detected, the control circuit 28 connects the switch 25 from the loop side to the transmission buffer 24 and instructs the start of transmission to the transmission buffer 24. When the transmission is finished, the control circuit 28 sends a token frame from a token transmission circuit 27. After the transmission, the switch 26 is connected to the loop and the state is restored to the original state.