FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See section 10, Rule 13] DECODING DEVICE, ENCODING DEVICE, AND METHODS FOR SAME; PANASONIC CORPORATION, A CORPORATION ORGANIZED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 1006, OAZA KADOMA, KADOMA-SHI, OSAKA 571-8501, JAPAN THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT !S TO BE PERFORMED. DESCRIPTION Technical Field The claimed invention relates to a decoding apparatus, an encoding apparatus, a decoding method and an encoding method that are used in a communication system encoding and transmitting a signal. Background Art For transmitting a speech or audio signal in a packet communication system represented by an Internet communication or a mobile communication system and/or the like, compression/encoding techniques are widely used to improve transmission efficiency of the speech or audio signal. Furthermore, in recent years, although speech or audio signals are simply encoded at a low bit rate, there is a growing demand for a technique for encoding a wider band speech/audio signal. In response to such a demand, various techniques for encoding a wide band speech or audio signal without drastically increasing the amount of encoded information are being developed. According to a technique disclosed in Patent Literature 1, and/or the like, an encoding apparatus calculates parameters to generate a spectrum of a high-frequency portion of a frequency of spectral data obtained by converting input acoustic signals corresponding to a certain time and outputs the parameters together with encoded information of a low-frequency portion. More specifically, the encoding apparatus divides the spectral data of the high-frequency portion of the frequency into a plurality of sub bands and calculates in each subband, a parameter that identifies a spectrum of the low-frequency portion most approximate to the spectrum of the subband. Next, the encoding apparatus adjusts the spectrum of the most approximate low-frequency portion using two types of scaling factors so that the peak amplitude in the high-frequency spectrum generated or energy of the subband (hereinafter, referred to as "subband energy") and the shape thereof become close to the peak amplitude, subband energy and shape of the spectrum of the high-frequency portion of a target input signal. Citation Li st Patent Literature PTL 1 International Publication WO2007/052088 Summary of Invention Technical Problem However, according to above-described Patent Literature 1, when combining high-frequency spectra, the encoding apparatus performs logarithmic transform on all samples (i.e., Modified Discrete Cosine Transform (MDCT) coefficients) of spectral data of an input signal and combined high-frequency spectral data. The encoding apparatus calculates parameters so that the subband energy and shape become close to the peak amplitude, subband energy and shape of the spectrum of the high-frequency portion of the target input signal. For this reason, there arises a problem that the amount of calculation of the encoding apparatus is considerably large. Furthermore, the decoding apparatus applies the calculated parameters to all samples in the subband without taking into consideration the magnitudes of amplitude of individual samples. Accordingly, the amount of calculation in the decoding apparatus for generating a high-frequency spectrum using the calculated parameters is very large, and the quality of the decoded speech thus generated is insufficient, and abnormal sound may also be produced in some instances. It is an object of the claimed invention to provide a decoding apparatus, an encoding apparatus, a decoding method and an encoding method that are capable of efficiently encoding spectral data in a high-frequency portion based on spectral data in a low-frequency portion of a wide band signal and thereby improving quality of a decoded signal. Solution to Problem A decoding apparatus according to a first aspect of the claimed invention is a decoding apparatus that adopts a configuration including: a receiving section that receives first encoded information indicating a low-frequency portion no greater than a predetermined frequency of a speech signal or an audio signal, band information for estimating a spectrum of a high-frequency portion higher than the predetermined frequency of the speech signal or the audio signal in a plurality of subbands obtained by dividing the high-frequency portion, and second encoded information containing a first amplitude adjusting parameter that adjusts the amplitude corresponding to a part or all of spectral components in each subband; a first decoding section that decodes the first encoded information to generate a first decoded signal; and a second decoding section that estimates the high-frequency portion of the speech signal or the audio signal from the first decoded signal using the second encoded information and adjusts the amplitude of the spectral component to thereby generate a second decoded signal, in which the. second decoding section includes: a spectral component selection section that selects 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 applies a second amplitude adjusting parameter to the selected part of the spectral components; and a second amplitude adjusting parameter application section that applies a third amplitude adjusting parameter adaptively set in accordance with the value of the second amplitude adjusting parameter for the spectral component that has not been selected. An encoding apparatus according to a second aspect of the claimed invention is an encoding apparatus that adopts a configuration including: a first encoding section that encodes a low-frequency portion no greater than a predetermined frequency of an input signal to generate first encoded information; a decoding section that decodes the first encoded information to generate a first decoded signal; a second encoding section that generates second encoded information containing band information for estimating a spectrum of a high-frequency portion higher than the predetermined frequency of the input signal in a plurality of subbands obtained by dividing the high-frequency portion and a first amplitude adjusting parameter that adjusts the amplitude corresponding to a part or all of spectral components in each subband; a second decoding section that estimates the high-frequency portion of the input signal from the first decoded signal using the second encoded information and adjusts the amplitude of the spectral component to thereby generate a second decoded signal; and a third encoding section that encodes a difference signal between the first decoded signal and the second decoded signal, and the input signal to generate third encoded information, in which the second decoding section includes: a spectral component selection section that selects a part of the spectral components for the spectrum of the estimated high-frequency portion of the input signal; a first amplitude adjusting parameter application section that applies a second amplitude adjusting parameter to the selected part of the spectral components; and a second amplitude adjusting parameter application section that applies a third amplitude adjusting parameter adaptively set in accordance with the value of the second amplitude adjusting parameter to a part of the spectral components that has not been selected. A decoding method according to a third aspect of the claimed invention adopts a configuration including: a receiving step of receiving first encoded information indicating a low-frequency portion no greater than a predetermined frequency of a speech signal or an audio signal, band information for estimating a spectrum of a high-frequency portion higher than the predetermined frequency of the speech signal or the audio signal in a plurality of subbands obtained by dividing the high-frequency portion, and second encoded information containing a first amplitude adjusting parameter that adjusts the amplitude corresponding to a part or all of spectral components in each subband; a first decoding step of decoding the first encoded information to generate a first decoded signal; and a second decoding step of estimating the high-frequency portion of the speech signal or the audio signal from the first decoded signal using the second encoded information and adjusting the amplitude of the spectral component to thereby generate a second decoded signal, in which the second decoding step includes: a spectral component selecting step of selecting 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 applying step of applying a second amplitude adjusting parameter to the selected part of the spectral components; and a second amplitude adjusting parameter applying step of applying a third amplitude adjusting parameter adaptively set in accordance with the value of the second amplitude adjusting parameter for a part of the spectral components that has not been selected. An encoding method according to a fourth aspect of the claimed invention adopts a configuration including: a first encoding step of encoding a low-frequency portion no greater than a predetermined frequency of an input signal to generate first encoded information; a decoding step of decoding the first encoded information to generate a first decoded signal; a second encoding step of generating second encoded information containing band information for estimating a spectrum of a high-frequency portion higher than the predetermined frequency of the input signal in a plurality of subbands obtained by dividing the high-frequency portion and a first amplitude adjusting parameter that adjusts the amplitude corresponding to a part or all of spectral components in each subband; a second decoding step of estimating the high-frequency portion of the input signal from the first decoded signal using the second encoded information and adjusting the amplitude of the spectral component to thereby generate a second decoded signal; and a third encoding step of encoding a difference signal between the first decoded signal and the second decoded signal, and the input signal to generate third encoded information, in which the second decoding step includes: a spectral component selecting step of selecting a part of the spectral components for the spectrum of the estimated high-frequency portion of the input signal; a first amplitude adjusting parameter applying step of applying a second amplitude adjusting parameter to the selected part of the spectral components; and a second amplitude adjusting parameter applying step of applying a third amplitude adjusting parameter adaptively set in accordance with the value of the second amplitude adjusting parameter to a part of the spectral component that has not been selected. Advantageous Effects of Invention According to the claimed invention, it is possible to efficiently encode/decode spectral data of a high-frequency portion of a wide band signal, realize a drastic reduction of the amount of calculation processing and improve the quality of the decoded signal. Brief Description of Drawings FIG.l is a block diagram showing a configuration of a communication system including an encoding apparatus and a decoding apparatus according to Embodiment 1 of the claimed invention; FIG.2 is a block diagram showing a principal internal configuration of the encoding apparatus shown in FIG.l according to Embodiment 1 of the claimed invention; FIG.3 is a block diagram showing a principal internal configuration of the second layer encoding section shown in FIG.2 according to Embodiment 1 of the claimed invention; FIG. 4 is a block diagram showing a principal configuration of the gain encoding section shown in FIG. 3 according to Embodiment 1 of the claimed invention; FIG. 5 is a block diagram showing a principal configuration of the logarithmic gain encoding section shown in FIG.4 according to Embodiment 1 of the claimed invention; FIG.6 is a diagram showing details of filtering processing in the filtering section according to Embodiment 1 of theclaimed invention; FIG.7 is a flowchart showing a procedure for processing of searching optimum pitch coefficient Tp" for subband SBp in the searching section according to Embodiment 1 of the claimed invention; FIG.8 is a block diagram showing a principal internal configuration of the decoding apparatus shown in F1G.1 according to Embodiment 1 of the claimed invention; FIG.9 is a block diagram showing a principal internal configuration of the second layer decoding section shown in FIG.8 according to Embodiment 1 of the claimed invention; FIG. 10 is a block diagram showing a principal internal configuration of the spectrum adjusting section shown in FIG.9 according to Embodiment 1 of the claimed invention; FIG. 11 is a block diagram showing a principal internal configuration of the logarithmic gain decoding section shown in FIG.10 according to Embodiment 1 of the claimed invention; FIG.12 is a diagram showing samples to which the logarithmic gain application section and the interpolation processing section in the logarithmic gain decoding section according to Embodiment 1 of the claimed invention are applied; FIG.13 is a block diagram showing the rest of the principal internal configuration of the encoding apparatus according to Embodiment 1 of the claimed invention; FIG. 14 is a block diagram showing a principal internal configuration of the encoding apparatus shown in FIG.l according to Embodiment 2 of the claimed invention; FIG. 15 is a block diagram showing a principal internal configuration of the second layer encoding section shown in FIG.14 according to Embodiment 2 of the claimed invention; FIG.16 is a block diagram showing a principal configuration of the first encoding section shown in FIG. 15 according to Embodiment 2 of the claimed invention; FIG.17 is a block diagram showing a principal internal configuration of. the decoding apparatus shown in FIG.l according to Embodiment 2 of the claimed invention; and FIG.18 is a block diagram showing a principal internal configuration of the second layer decoding section shown in FIG.17 according to Embodiment 2 of the claimed invention. Description of Embodiments According to the claimed invention, when generating spectral data of a high-frequency portion of a signal to be encoded based on spectral data of a low-frequency portion, an encoding apparatus calculates sub band energy and shape adjusting parameters for a sample group extracted based on the position of a sample having a maximum amplitude in the subband. Furthermore, a decoding apparatus applies the parameters to the sample group extracted based on the sample position where amplitude is a maximum in the subband. Thus, it is possible to efficiently encode/decode spectral data in the high-frequency portion of a wide band signal, realize a drastic reduction of the amount of calculation processing, and also improve the quality of the decoded signal. Hereinafter, embodiments of the claimed invention will be described in detail with reference to the accompanying drawings. Suppose the encoding apparatus and the decoding apparatus according to the claimed invention target any of a speech signal, an audio signal and a combination thereof as an input signal/output signal. Each embodiment of the claimed invention will describe a speech encoding apparatus and a speech decoding apparatus as examples. (Embodiment 1 ) FIG.l is a block diagram showing a configuration of a communication system including the encoding apparatus and the decoding apparatus according to the present embodiment. In FIG.l, the communication system is provided with encoding apparatus 101 and decoding apparatus 103, each of which can communicate with each other via transmission path 102. Both encoding apparatus 101 and decoding apparatus 103 are usually used while installed on a base station apparatus or communication terminal apparatus and/or the like. Encoding apparatus 101 divides an input signal into blocks of N samples (N is a natural number) and performs encoding for each frame including N samples. Let us suppose that an input signal to be encoded is expressed by xn (n = 0, ..., N-l), where n denotes an (n + 1)th signal element of the input signal divided into N-sample blocks. Encoding apparatus 101 transmits the encoded input information (i.e., encoded information) to decoding apparatus 103 via transmission path 102. Decoding apparatus 103 receives the encoded information transmitted from encoding apparatus 101 via transmission path 102 and decodes the encoded information to obtain an output signal. FIG.2 is a block diagram showing a principal internal configuration of encoding apparatus 101 shown in FIG.l. Assuming that a sampling frequency of the input signal is SRi, downsampling processing section 201 downsamples the sampling frequency of the input signal from S R i to SR2 (SR20) and sets Signp(k) = -1 otherwise (when the sign of the extracted sample is '-')• [20] Logarithm ic gain application section 3 73 calculates estimated spectrum S5'(k) according to equation 21 and equation 22 for a sample having an extraction flag SelectFlag(k) value of 1 based on estimated spectrum S3'(k) inputted from sample group extraction section 372, maximum amplitude value MaxValuep and extraction flag SelectFlag(k), quantized logarithmic gain α2Qp inputted from gain decoding section 354 and code Signp(k) calculated according to equation 20. [21] ... (Equation 21) [22] S5ik) = lOS4'(k)-Signp(k) {BLp