In an optical pulse demultiplexer according to the invention, an optical splitter splits an input pulse signal light having a signal wavelength into a firs portion and a second portion. An optical clock generator generates an optical clock having a clock wavelength at a predetermined frequency corresponding to 1/n (n is integer not less than 2) of a bit rate of the input pulse signal light out of the first portion of the output lights from the optical splitter. The clock wavelength is different from the signal wavelength. A saturable absorption optical element, to which the optical clock generated by the optical clock generator and the second portion enter, separates a channel component corresponding to the predetermined frequency out of the second according to the optical clock. An optical filter extracts an optical component of the signal wavelength out of the light output from the saturable absorption optical element. A nonlinear waveform shaper suppresses a low level part of the light output from the first optical filter.