PURPOSE: To prevent noises and jitters from appearing in a synchronous reproduction output by extracting a clock from only a data input signal when a binary signal indicates a light input above a specific level and feeding the output of a clock extraction part back to an input side when below the specific level.

CONSTITUTION: When the light input from an optical fiber cable exceeds the specific level, the output of a full-wave rectifying circuit 3 and the input of a resonance circuit 4 are connected electrically and the output of a feedback circuit 6 and the resonance circuit 4 are disconnected electrically. A differential pulse corresponding to a data input signal is generated by a differentiating circuit 2 and supplied to the resonance circuit 4. Consequently, a clock extraction part 10 extracts a timing clock having no jitters without being affected by the feedback circuit 6. When the light input does not exceeds the specific level, the output terminal of the feedback circuit 6 is connected electrically to the input terminal of the resonance circuit 4 and the output terminal of the full-wave rectifying circuit 3 and the input terminal of the resonance circuit are disconnected.