PURPOSE: To quicken the signal processing with simple constitution by providing an optical amplifier, an optical branch circuit, an optical clock extraction circuit, a optical confluencing circuit and an optical identification circuit and using them so as to process the 3R functions as the repeater at an optical level.

CONSTITUTION: An optical input data signal is waveform-shaped by an optical amplifier 1 an branched into two at an optical branch circuit 2. On the other hand, one branch optical data signal is subject to optical clock signal extraction by an optical clock extraction circuit 3 to apply retiming. Furthermore, the other branched optical data signal is retarded so as to match the phase of the circuit 3 at the optical delay element 4. Then the output from the circuits 3, 4 is confluenced by the optical confluencing circuit 5 and identified at a prescribed optical threshold level by an optical identification circuits 6 and the optical data is reproduced. Then the 3R functions such as waveform shaping, retiming and repeater for identification and reproduction are processed entirely by the optical level in this way, then the signal processing is quickened with simple constitution.