A decoding apparatus comprising: a receiving section that is adapted to receive first encoded information indicating a low-frequency portion no greater than a predetermined frequency of a speech signal or an audio signal, and second encoded information, the second encoded information containing band information for estimating a spectrum of a high-frequency portion of the speech signal or the audio signal in a plurality of subbands obtained by dividing the high-frequency portion higher than the predetermined frequency, and a first amplitude adjusting parameter that is adapted to adjust an amplitude corresponding to a part or all of spectral components in each subband; a first decoding section that is adapted to decode the first encoded information to generate a first decoded signal; and a second decoding section that is adapted to estimate the high-frequency portion of the speech signal or the audio signal from the first decoded signal using the second encoded information and adjust the amplitude of the spectral component to thereby generate a second decoded signal, wherein the second decoding section comprises: a spectral component selection section that is adapted to select a part of the spectral components for the spectrum of the estimated high-frequency portion of the speech signal or the audio signal; a first amplitude adjusting parameter application section that is adapted to apply a second amplitude adjusting parameter to the selected part of the spectral components; and a second amplitude adjusting parameter application section that is adapted to apply a third amplitude adjusting parameter adaptively set in accordance with the value of the second amplitude adjusting parameter, to the spectral component that has not been selected, wherein the second amplitude adjusting parameter application section is adapted to set the third amplitude adjusting parameter to a smaller value when the value of the second amplitude adjusting parameter is smaller than a predetermined threshold, and set the third amplitude adjusting parameter to a larger value when the value of the second amplitude adjusting parameter is no less than the predetermined threshold. a receiving section that is adapted to receive first encoded information indicating a low-frequency portion no greater than a predetermined frequency of a speech signal or an audio signal, and second encoded information, the second encoded information containing band information for estimating a spectrum of a high-frequency portion of the speech signal or the audio signal in a plurality of subbands obtained by dividing the high-frequency portion higher than the predetermined frequency, and a first amplitude adjusting parameter that is adapted to adjust an amplitude corresponding to a part or all of spectral components in each subband; a first decoding section that is adapted to decode the first encoded information to generate a first decoded signal; and a second decoding section that is adapted to estimate the high-frequency portion of the speech signal or the audio signal from the first decoded signal using the second encoded information and adjust the amplitude of the spectral component to thereby generate a second decoded signal, wherein the second decoding section comprises: a spectral component selection section that is adapted to select a part of the spectral components for the spectrum of the estimated high-frequency portion of the speech signal or the audio signal; a first amplitude adjusting parameter application section that is adapted to apply a second amplitude adjusting parameter to the selected part of the spectral components; and a second amplitude adjusting parameter application section that is adapted to apply a third amplitude adjusting parameter adaptively set in accordance with the value of the second amplitude adjusting parameter, to the spectral component that has not been selected, wherein the second amplitude adjusting parameter application section is adapted to set the third amplitude adjusting parameter to a smaller value when the value of the second amplitude adjusting parameter is smaller than a predetermined threshold, and set the third amplitude adjusting parameter to a larger value when the value of the second amplitude adjusting parameter is no less than the predetermined threshold. a spectral component selection section that is adapted to select a part of the spectral components for the spectrum of the estimated high-frequency portion of the speech signal or the audio signal; a first amplitude adjusting parameter application section that is adapted to apply a second amplitude adjusting parameter to the selected part of the spectral components; and a second amplitude adjusting parameter application section that is adapted to apply a third amplitude adjusting parameter adaptively set in accordance with the value of the second amplitude adjusting parameter, to the spectral component that has not been selected, wherein the second amplitude adjusting parameter application section is adapted to set the third amplitude adjusting parameter to a smaller value when the value of the second amplitude adjusting parameter is smaller than a predetermined threshold, and set the third amplitude adjusting parameter to a larger value when the value of the second amplitude adjusting parameter is no less than the predetermined threshold.