Provided is a spectrum analysis method including: accumulating n spectrums obtained by consecutively fast Fourier transforming an input signal n times; receiving a threshold; identifying, in the n spectrums accumulated in the accumulating, frequently occurring data that includes data whose number of occurrences exceeds the threshold received in the receiving, the number of occurrences being defined as a total number of items of data at a same frequency point that indicate levels that are close to each other, to within a predetermined range; selecting a maximum level at each of the frequency points from among only the identified frequently occurring data; and outputting a spectrum indicating the maximum levels selected at the frequency points.