An amplitude adjustment circuit includes a memory that stores correspondence information between frequency distributions of an amplitude and adjustment coefficients, a processor configured to generate a frequency distribution of amplitude of data for which adaptive equalization processing has been executed, acquire the correspondence information between frequency distributions of the amplitude and adjustment coefficients from the memory, select the adjustment coefficient based on a result of comparison between the frequency distributions included in the correspondence information acquired by the acquiring unit and the frequency distribution generated by the generating unit, and adjust a gain of the data based on the adjustment coefficient selected by the selecting unit.