Abstract: A multiplex transmission system, in which one of a plurality of nodes, as a transmission node, mutually coupled together through a transmission path transmits data frame by frame to at least one of other nodes as at least one of reception node, and the reception node returns a reception acknowledge signal to the transmitting node upon proper reception of the frame of data. A reception acknowledge signal area comprising a plurality of bits is provided following the frame transmitted from the transmitting node. The reception acknowledge signal area is divided into a plurality of bit areas which are respectively assigned to the plurality of nodes. The reception node returns the reception acknowlege signal to the transmitting node from the respectively-assigned bit areas of the reception acknowledge signal area.