PURPOSE: To always and normally transmit data by switching the data transmitted from a prestage equipment and the data in a present transmitter, timing- regenerating the output and a frame pulse by means of a clock and outputting them to an equipment in a subsequent stage.

CONSTITUTION: A receiver 1 outputs a clock (a) generated in a clock generation circuit 3 and the frame pulse (b) to a transmitter 2a. The transmitter 2a receives the clock (a) and the frame pulse (b) in a transmission timing generation circuit 6, decides the timing transmitting data of its own equipment and transmits it to a switching circuit 7. The switching circuit 7 changes over the data from a previous stage in accordance with the timing with the data of the its own equipment and outputs it to a timing reproduction circuit 8. The timing reproduction circuit 8 timing-reproduces the frame pulse (b) and the output of the switching circuit 7 in accordance with the clock (a), and outputs them to a transmitter 2b in the subsequent stage. Thus, data is always and normally transmitted regardless of the distance between the receiver 1 and the transmitter 2 or the number of the transmitters.