To provide an optical signal processor which increases a processing speed, can be miniaturized and does not depend upon a polarized state of an optical signal.

An optical path superimposer/separator 10 once superimposes optical paths of inputted two beams of signal light and then separates the optical paths. A nonlinear waveguide is arranged at part where both optical paths are superimposed. First and second optical waveguides are connected to the optical path superimposer/ separator. The optical path length of the second optical waveguide 3 is longer than that of the first optical waveguide 2. A control light introduction optical system introduces control light to the nonlinear waveguide. An interference separator 24 allocates the signal light on the basis of the phase difference between two beams of signal light to be inputted. Third and fourth optical waveguides 22 and 23 connect the optical path superimposer/separator and the interference separator. The optical path lengths of the third and fourth optical waveguides are set up so as to recover delay time when signal light propagating the second optical waveguide delays with respect to signal light propagating the first optical waveguide at a point of time when the signal light reaches the interference separator.