A processing device according to this embodiment includes: a frequency characteristics acquisition unit configured to acquire frequency characteristics of an input signal; an extreme value extraction unit configured to extract an extreme value of spectral data; a kurtosis calculation unit configured to: calculate an evaluation value from spectral data; and calculate a kurtosis of a peak or a dip based on a plurality of evaluation values calculated by changing a calculation width, the evaluation value being used for evaluating the peak or the dip corresponding to the extreme value; a determination unit configured to determine whether to suppress the peak or the dip according to a comparison result between the kurtosis and a threshold value; and a suppression unit configured to suppress the peak or the dip with the extreme value that is determined to be suppressed.