1. A classification apparatus comprising: a template image memorizing unit that stores an image of a two-dimensional Fourier transform of a spectrogram of a time variation signal detected in relation to a phenomenon, as a template image, with regard to each of one or more phenomena; a spectrogram generation unit that generates the spectrogram of the time variation signal of a classification object by processing the time variation signal of the classification object obtained by a sensor; a two-dimensional Fourier transform calculation unit that calculates the two-dimensional Fourier transform of the spectrogram generated by the spectrogram generation unit; a similarity calculation unit that calculates a similarity between the template image and an image of the two-dimensional Fourier transform obtained by the two-dimensional Fourier transform calculation unit, for each template image corresponding to each phenomenon stored in the template image memorizing unit; and a determination unit that determines whether the time variation signal of the classification object conforms to any of one or more phenomena, on the basis of the similarity calculated by the similarity calculation unit.