An equalizer apparatus includes a feedforward filter, a slicer circuit and a feedback circuit. The feedforward filter processes an input signal. The slicer circuit includes a Viberbi decoding circuit coupled to the feedforward filter, and performs a Viberbi algorithm based decision operation to generate a decision signal according to an output signal of the feedforward filter and a feedback signal of the feedback filter. The feedback filter generates the feedback signal according to the decision result signal.