A multiplex transmission system, in which a node as a transmission node transmits data frame by frame to a transmission path, and a plurality of other nodes, as reception nodes, returns a reception acknowledgment signal to the transmission path upon proper reception of the frame of data. Each of the reception nodes which properly received the frame returns the reception acknowledgment signal specific thereto to that division of a reception acknowledgment signal area in the frame which corresponds to this node. Each node discriminates the success/failure of signal transmission, by comparing the information registered beforehand in its reception acknowledgment signal table with the information in the reception acknowledgment signal area. When the information of the reception acknowledgment signal table does not coincide with that of the reception acknowledgment signal area, the transmission node re-transmits the frame and the reception acknowledgment signal tables of all the nodes are updated. The system can not only effect the addition and deletion of multiplex nodes easily without requiring the change of scale of the circuit of the system, but also discriminate trouble for each of the multiplex nodes.