When restoring signals from an optical recording medium, one usually obtains nonlinearly distorted signals. The equalizer disclosed in the prior art can only process linear signals. A new structure that can process nonlinearly distorted signals is disclosed, which including an A/D converter for sampling restoring signals. The restored signals are processed by an adaptive linear equalizer to extract the errors. The errors are then fed into a nonlinear equalizer for correcting the nonlinear distortion.