Abstract: A data transmission system comprising a unidirectional loop transmission path to which a plurality of communication equipment are coupled. Each communication equipment operates to relay and send a signal including a data signal received from other communication equipment located upstream to those located downstream via the transmission path. An arbitrary communication equipment which requests for the sending right adds a code indicating a priority level of the sending right to a sending right request signal and sends this code-added sending right request signal. Each communication equipment includes a circuit which delays the received signal by a predetermined time shorter than a frame time and sends the signal thus delayed.