PURPOSE: To provide the equalizer to obtain an excellent equalization signal even when the state of a transmission line is unstable.

CONSTITUTION: The equalizer in which a reproduction signal from an adaptive filter section 10 is discriminated by a discriminator 12 based on a prescribed criterion and which controls a filter coefficient of the adaptive filter section 10 so as to minimize an error signal being a difference between a discrimination output and a reproduction signal from the adaptive filter section 10, is provided with buffer memories 24,26,28 storing respectively an input signal, a discrimination output and the error signal, and a selection circuit 31 which applies forward processing to the input signal to obtain a 1st reproduction signal and a 1st error signal, then applies backward processing to the input signal to obtain a 2nd reproduction signal and a 2nd error signal, comparing 1st and 2nd averaging outputs resulting from averaging the 1st and 2nd error signals separately over a prescribed period with an upper limit threshold level and a lower limit threshold level and outputs either of the 1st and 2nd reproduction signals as an equalizing signal based on the result of comparison.