1. A feature extraction apparatus which acquires a feature value for AAC-format song data, the feature extraction apparatus including: an MDCT coefficient extraction unit which extracts MDCT coefficients from the AAC-format song data, the AAC-format song data being stored on a storage unit; a classification unit which locates the MDCT coefficients thus extracted by the MDCT coefficient extraction unit on Mel frequency regions so as to uniformly classify the MDCT coefficients into classes, the number of which is the same as that of a predetermined number of Mel filter banks; an integrating unit which extracts the MDCT coefficients classified by the classification unit by applying a predetermined window function, and integrates the MDCT coefficients thus extracted, in increments of the Mel filter banks; and a feature calculation unit which calculates the feature value by performing logarithmic cosine conversion of the integrated results obtained by the integrating unit; wherein the classification unit includes: a Mel frequency calculation unit which converts the sampling frequency for the AAC-format song data into a Mel scale, thereby obtaining a Mel frequency, a Mel frequency dividing unit which divides the Mel frequency into the same number of classes as that of the Mel filter banks, and calculates the minimum value and the maximum value for each of the Mel frequencies thus divided, an original frequency calculation unit which converts the minimum value and the maximum value of each Mel frequency calculated by the Mel frequency dividing unit into a linear scale, thereby obtaining the minimum value and the maximum value for each original frequency; an upper-limit frequency calculation unit which calculates the upper-limit frequency based upon the sampling frequency for the AAC-format song data, an upper-limit frequency dividing unit which uniformly divides the upper-limit frequency calculated by the upper-limit frequency calculation unit into frequency bands, the number of which is the same as a predetermined number of filter banks, a center frequency classification unit which classifies the center frequencies of the frequency bands into regions each of which is defined by the minimum value and the maximum value of the original frequency, thereby classifying the center frequencies into the same number of classes as that of the Mel filter banks, and an MDCT coefficient classification unit which classifies the MDCT coefficients, which have been extracted by the MDCT coefficient extraction unit and the number of which is the same as that of the filter banks, into the same number of classes as that of the Mel filter banks, by associating each MDCT coefficient with a corresponding one of the center frequencies which have been classified by the center frequency classification unit into the same number of classes as that of the Mel filter banks; and wherein the integrating unit extracts the MDCT coefficients classified by the MDCT coefficient classification unit by applying the predetermined window function, and integrates the MDCT coefficients thus extracted, in increments of the Mel filter banks.