It becomes difficult to perform the optimum equalization signal processing in coherent receiving systems if a channel response in an optical fiber transmission line includes a factor without temporal centrosymmetry, therefore, an equalization signal processor according to an exemplary aspect of the invention includes an equalization filter means configured to receive digital signals by coherent receiving systems; a coefficient control means configured to control coefficients defining characteristics of the equalization filter means; a significant coefficient holding means configured to hold significant coefficients of significant values among initial values of the coefficients; a significant coefficient positioning means configured to determine a significant coefficient position, a position of the significant coefficients in the initial values, so that equalization characteristics of the equalization filter means may be optimized; and a significant coefficient setting means configured to allocate the significant coefficients to the significant coefficient position.