An optical digital regenerator for digitally regenerating an input signal in an intact optical state. A first operating unit has a first probe light generator for generating a first probe light and a first optical operator for converting a waveform of the first probe light output from a first probe light generator according to an optical intensity waveform of the input signal light. A clock extractor extracts a clock component of the input signal light from a photocurrent generated by the first optical operator. A second optical operating unit has a second probe light generator for generating a second probe light pulsed in accordance with the clock output from the clock extractor and a second optical operator for sampling the second probe pulse light output from the second probe light generator.