An audio signal decoding apparatus comprising: a demultiplexing section that demultiplexes encoding parameters, index information that identifies the most correlated portion from the low frequency spectrum for one or more high frequency subbands, and scale factor information from encoded information; a spectrum replication section that replicates a high frequency subband spectrum based on the index information using a synthesized low frequency spectrum, the synthesized low frequency spectrum being obtained by decoding the encoding parameters; and a spectrum envelope adjustment section that adjusts an amplitude of the replicated high frequency subband spectrum using the scale factor information, a harmonic frequency estimation section that estimates a frequency of a harmonic component in the synthesized low frequency spectrum; a harmonic frequency adjustment section that adjusts a frequency of a harmonic component in the high frequency subband spectrum using the estimated harmonic frequency; and an output section that generates an output signal using the synthesized low frequency spectrum and the high frequency subband spectrum. wherein the harmonic frequency estimation section comprises: a splitting section that splits a preselected portion of the synthesized low frequency spectrum into plural blocks; a spectral peak identification section that identifies a frequency of a spectral peak having a maximum amplitude in each of the plural blocks; a spacing calculation section that calculates spacing values between each of the identified spectral peak frequencies; and a harmonic frequency calculation section that calculates the harmonic frequency using the spacing values between the identified spectral peak frequencies. a demultiplexing section that demultiplexes encoding parameters, index information that identifies the most correlated portion from the low frequency spectrum for one or more high frequency subbands, and scale factor information from encoded information; a spectrum replication section that replicates a high frequency subband spectrum based on the index information using a synthesized low frequency spectrum, the synthesized low frequency spectrum being obtained by decoding the encoding parameters; and a spectrum envelope adjustment section that adjusts an amplitude of the replicated high frequency subband spectrum using the scale factor information, a harmonic frequency estimation section that estimates a frequency of a harmonic component in the synthesized low frequency spectrum; a harmonic frequency adjustment section that adjusts a frequency of a harmonic component in the high frequency subband spectrum using the estimated harmonic frequency; and an output section that generates an output signal using the synthesized low frequency spectrum and the high frequency subband spectrum. wherein the harmonic frequency estimation section comprises: a splitting section that splits a preselected portion of the synthesized low frequency spectrum into plural blocks; a spectral peak identification section that identifies a frequency of a spectral peak having a maximum amplitude in each of the plural blocks; a spacing calculation section that calculates spacing values between each of the identified spectral peak frequencies; and a harmonic frequency calculation section that calculates the harmonic frequency using the spacing values between the identified spectral peak frequencies. a splitting section that splits a preselected portion of the synthesized low frequency spectrum into plural blocks; a spectral peak identification section that identifies a frequency of a spectral peak having a maximum amplitude in each of the plural blocks; a spacing calculation section that calculates spacing values between each of the identified spectral peak frequencies; and a harmonic frequency calculation section that calculates the harmonic frequency using the spacing values between the identified spectral peak frequencies.