PURPOSE: To absorb a data delay time even when the number of transmission lines is increased and to attain multiplexing by detecting a frame pattern of each transmission line, storing a frame data to a memory, absorbing a delay between data and multiplexing the result.

CONSTITUTION: When a data with a flame pulse is inputted from each transmission line to frame pattern detection sections 21a-21n and they detect a frame pattern, output a frame detection signal and write a bit data to a relevant memory 22a. A multiplexer section 25 changes over the connection of lines based on the output sequence from the detection sections 21a-21n to allow a data outputted in the n-th order to appear at a line On. As a result, when a parallel serial conversion section selects and outputs one bit data each in the order of lines 01→.... On, the data is rearranged serially in the order of demultiplexing in a transmitter 1 and the result is outputted to a high speed transmission line HW2. Every time a clock is generated, when the data is read and outputted to the line, the data is rearranged in the order of demultiplexing and the result is outputted as an original serial data.