The present invention provides an equalizer capable of accurately compensating for non-linearity of an input signal due to the asymmetry phenomenon, etc., during the disk production process. Two tap coefficients are provided in a coefficient unit. A comparator compares the value of a middle tap signal, which is a reference signal, and a threshold, so as to produce a selection signal based on the comparison result. The coefficient unit selects one of the two tap coefficients as the selected tap coefficient based on the selection signal, and a tap signal is multiplied with the selected tap coefficient. Thus, it is possible to adaptively switch the tap coefficients of the equalizer as a whole based on the value of the middle tap signal, which is the reference signal. Therefore, it is possible to accurately compensate for the non-linearity of the input signal.