To solve the problem of being incapable of flexibly changing a filter composition according to a requested characteristic since a filter circuit for an equalizer is conventionally fixed.

The equalizer includes: the filter circuit which can implement a plurality of filter shapes by changing over connection for a delay tap; an error calculation circuit for deriving an error between an output value and an expectation value for the output value of the filter circuit; a coefficient calculation circuit for updating a filter coefficient for the filter circuit by a prescribed algorithm in the direction reducing the error and setting to the filter circuit; and a control circuit for specifying the filter shape in order from a plurality of filter shapes, acquiring the error when the error calculation circuit is converged and the filter coefficient when converged for every filter shape, selecting the filter shape corresponding to a relatively small error when compared to a plurality of errors acquired for every filter shape, as well as setting the filter coefficient for the converged time corresponding to the selected filter shape to the filter circuit.