FORM 2 THE PATENTS ACT, 1970 (39 Of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See section 10, Rule 13] ENCODER, DECODER, AND METHOD THEREFOR; PANASONIC CORPORATION, A CORPORATION ORGANIZED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 1006, OAZA KADOMA, KADOMA-SHI, OSAKA 5718501, JAPAN THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED. DESCRIPTION Technical Field The present invention relates to an encoding apparatus, a decoding apparatus, and a method therefor that are used for a communication system which transmits a signal by encoding the signal. Background Art When speech or sound signals are transmitted by a packet communication system, a mobile communication system, or the like as represented by Internet communications, compressing and encoding techniques are often used to increase transmission efficiency of the speech or sound signals. Further, in recent years, while encoding speech or sound signals at simply a low bit rate, there is an increasing demand for a technique of encoding speech or sound signals of a broader band. To meet this need, various techniques have been developed to encode broadband speech or sound signals without substantially increasing the amount of information after encoding. For example, according to a technique disclosed in Patent Literature 1, an encoding apparatus calculates a parameter to generate a spectrum of a high frequency part out of spectrum data obtained by converting an input acoustic signal for a constant time period, and outputs this parameter by matching this with encoded information of a low frequency part. Specifically, the encoding apparatus divides the spectrum data of a high frequency part of a frequency into a plurality of sub-bands, and calculates a parameter that specifies a spectrum of a low frequency part that is most similar to the spectrum of each sub-band. Next, the encoding apparatus adjusts the most similar spectrum of a low frequency part by using two kinds of scaling factors such that a peak amplitude, or energy of a sub-band (hereinafter, "sub-band energy") and a shape in a high-frequency spectrum to be generated becomes similar to a peak amplitude, sub-band energy, and a shape of a spectrum of a high frequency part of an input signal as a target. Citation List Patent Literature PTL 1 WO Publication No. 2007/052088 Summary of Invention Technical Problem However, according to the above-described Patent Literature 1, in combining a high-frequency spectrum, the encoding apparatus performs a logarithmic transform to all samples (MDCT coefficients) of spectrum data of an input signal and combined high-frequency spectrum data. Then, the encoding apparatus calculates a parameter such that respective sub-band energy and shapes becomes similar to a peak amplitude, sub-band energy, and a shape of a high-frequency spectrum of the input signal as the target. Therefore, there is a problem that the volume of arithmetic operations in the encoding apparatus is very large. Further, the encoding apparatus applies a calculated parameter to all samples within the sub-bands, and does not take into account sizes of amplitudes of individual samples. Consequently, the volume of arithmetic operations in the encoding apparatus when generating a high-frequency spectrum by using the calculated parameter also becomes very large. Further, quality of decoded speech to be generated is insufficient, and there is a possibility that abnormal sound is generated depending on the case. It is therefore an object of the present invention to provide an encoding apparatus, a decoding apparatus and a method therefor capable of efficiently encoding spectrum data of a high frequency part and improving quality of a decoded signal based on spectrum data of a low frequency part of a broadband signal. Solution to Problem The encoding apparatus of the present invention is configured to include: first encoding means for generating first encoded information by encoding a lower frequency part equal to or lower than a predetermined frequency of an input signal; decoding means for generating a decoded signal by decoding the first encoded information; and second encoding means for generating second encoded information by dividing a high frequency part of the input signal higher than the predetermined frequency into a plurality of sub-bands, estimating the a plurality of sub-bands respectively from the input signal or the decoded signal, partially selecting a spectrum component within each of the sub-bands, and calculating an amplitude adjustment parameter for adjusting an amplitude for the selected spectrum component. The decoding apparatus of the present invention is configured to include: receiving means for receiving first encoded information obtained by encoding a lower frequency part of an input signal equal to or lower than a predetermined frequency generated by the encoding apparatus, and second encoded information generated by dividing a high frequency part of the input signal higher than the predetermined frequency into a plurality of sub-bands, estimating the a plurality of sub-bands respectively from the input signal or from a first decoded signal obtained by decoding the first encoded information, partially selecting a spectrum component within each of the sub-bands, and calculating an amplitude adjustment parameter for adjusting an amplitude for the selected spectrum component; first decoding means for generating a second decoded signal by decoding the first encoded information; and second decoding means for generating a third decoded signal by estimating a high frequency part of the input signal from the second decoded signal. The encoding method of the present invention includes: a step of generating first encoded information by encoding a lower frequency part of an input signal equal to or lower than a predetermined frequency; a step of generating a decoded signal by decoding the first encoded information; and a step of generating second encoded information by dividing a high frequency part of the input signal higher than the predetermined frequency into a plurality of sub-bands, estimating the a plurality of sub-bands respectively from the input signal or the decoded signal, partially selecting a spectrum component within each of the sub-bands, and calculating an amplitude adjustment parameter for adjusting an amplitude for the selected spectrum component. The encoding method of the present invention includes: a step of receiving first encoded information obtained by encoding a lower frequency part of an input signal lower than a predetermined frequency generated by the encoding apparatus, and second encoded information generated by dividing a high frequency part of the input signal higher than the predetermined frequency into a plurality of sub-bands, estimating the a plurality of sub-bands respectively from the input signal or from a first decoded signal obtained by decoding the first encoded information, partially selecting a spectrum component within each of the sub-bands, and calculating an amplitude adjustment parameter for adjusting an amplitude for the selected spectrum component; a step of generating a second decoded signal by decoding the first encoded information; and a step of generating a third decoded signal by estimating a high frequency part of the input signal from the second decoded signal. Advantageous Effects of Invention According to the present invention, spectrum data of a high frequency part of a broadband signal can be efficiently encoded/decoded, the volume of arithmetic operations can be substantially reduced, and quality of a decoded signal can be also improved. Brief Description of the Drawings FIG. 1 is a block diagram showing a configuration of a communication system that has an encoding apparatus and a decoding apparatus according to Embodiment 1 of the present invention; FIG.2 is a block diagram showing a relevant configuration of the inside of the encoding apparatus shown in FIG.l according to Embodiment 1 of the present invention; FIG.3 is a block diagram showing a relevant configuration of the inside of a second layer encoding section shown in FIG.2 according to Embodiment 1 of the present invention; FIG.4 is a block diagram showing a relevant configuration of a gain encoding section shown in FIG.3 according to Embodiment 1 of the present invention; FIG.5 is a block diagram showing a relevant configuration of a logarithmic gain encoding section shown in FIG.4 according to Embodiment 1 of the present invention; FIG.6 is a diagram for explaining a detail of a filtering process in a filtering section according to Embodiment 1 of the present invention; FIG. 7 is a flowchart showing a step of a process of searching for an optimal pitch coefficient TP' of a sub-band SBP in a search section according to Embodiment 1 of the present invention; FIG.8 is a block diagram showing a relevant configuration of the inside of the decoding apparatus shown in FIG.l according to Embodiment 1 of the present invention; FIG.9 is a block diagram showing a relevant configuration of the inside of a second layer decoding section shown in FIG.8 according to Embodiment 1 of the present invention; FIG.10 is a block diagram showing a relevant configuration of the inside of a spectrum adjusting section shown in FIG.9 according to Embodiment 1 of the present invention; FIG.11 is a block diagram showing a relevant configuration of the inside of a logarithmic gain decoding section shown in FIG.10 according to Embodiment 1 of the present invention; FIG.12 is a block diagram showing a relevant configuration of the inside of a second layer encoding section according to Embodiment 2 of the present invention; FIG.13 is a block diagram showing a relevant configuration of the inside of a gain encoding section shown in FIG. 12 according to Embodiment 2 of the present invention; FIG.14 is a block diagram showing a relevant configuration of the inside of a logarithmic gain encoding section shown in FIG.13 according to Embodiment 2 of the present invention; and FIG.15 is a block diagram showing a relevant configuration of the inside of a logarithmic gain decoding section according to Embodiment 2 of the present invention. Description of Embodiments A main characteristic of the present invention is that the encoding apparatus calculates an adjustment parameter of sub-band energy and a shape of a sample group that is extracted based on a position of a sample of a maximum amplitude within a sub-band, when the encoding apparatus generates spectrum data of a high frequency part of a signal to be encoded based on spectrum data of a low frequency part. Another main characteristic is that the decoding apparatus applies the calculated parameter to the sample group that is extracted based on the position of the sample of a maximum amplitude within the sub-band. Based on these characteristics of the present invention, spectrum data of a high frequency part of a broadband signal can be efficiently encoded/decoded, the volume of arithmetic operations can be substantially reduced, and quality of a decoded signal can be also improved. Embodiments of the present invention are explained in detail below with reference to drawings. A speech encoding apparatus and a speech decoding apparatus are explained as an example of the encoding apparatus and the decoding apparatus according to the present invention. (Embodiment 1) FIG.l is a block diagram showing a configuration of a communication system that has an encoding apparatus and a decoding apparatus according to Embodiment 1 of the present invention. In FIG.l, communication system includes encoding apparatus 101 and decoding apparatus 103, and they can communicate with each other via transmission channel 102. Both encoding apparatus 101 and decoding apparatus 103 are usually used by being mounted on a base station apparatus, a communication terminal device, or the like. Encoding apparatus 101 divides an input signal into each N samples (N is a natural number), and encodes each frame by setting N samples as one frame. An input signal to be encoded is expressed as xn (n = 0, ..., N-l). This n denotes an (n+l)-th order of a signal element of the input signal that is divided into each N samples. Encoding apparatus 101 transmits encoded input information (encoded information) to decoding apparatus 103 via transmission channel 102. Decoding apparatus 103 receives encoded information transmitted from encoding apparatus 101 via transmission channel 102. FIG.2 is a block diagram showing a relevant configuration of the inside of encoding apparatus 101 shown in FIG.l. When a sampling frequency of an input signal is SR1, down-sampling processing section 201 down-samples the sampling frequency of the input signal from SRi to SR2 (SR2 a predetermined filter coefficient pi, is substituted in S2p'(k). This process is expressed by following equation 15. The estimated spectrum S2p'(k) in BSp0), and calculates Signp(k)=-1 in other cases (when the sign of the extracted sample is "-" (when Signp(k)>0). [18] Logarithmic gain applying section 373 calculates a decoded spectrum S5'(k), following equations 19 and 20, for a sample where the value of the extraction flag SelectFlag(k) is 2, based on the estimated spectrum S3'(k), the maximum amplitude value MaxValuep, and the extraction flag SelectFlag(k) that are input from sample group extracting section 372, and based on the quantized logarithmic gain a2Qp that is input from gain decoding section 354, and the sign Signp(k) that is calculated following equation 1 8. [19] That is, logarithmic gain applying section 3 73 applies the logarithmic gain a2p to only a sample that is partially selected by sample extracting section 372 (a sample of the extraction flag SelectFlag(k=l). Logarithmic gain applying section 373 outputs the decoded spectrum S5'(k) to orthogonal transform processing section 356. In this case, a low frequency part (00), and calculates Signp(k)=-1 in other cases (when the sign of the extracted sample is "-" (when Signp(k)>0). Logarithmic gain applying section 383 calculates a decoded spectrum S5'(k), following equations 19 and 20, for a sample where the value of the extraction flag SelectFlag(k) is 1, based on the estimated spectrum S3'(k), the maximum amplitude value MaxValuepj and the extraction flag SelectFlag(k) that are input from sample group extracting section 382, and based on the quantized logarithmic gain a2Qp that is input from gain decoding section 354, and the sign Signp(k) that is calculated following equation 1 8. That is, logarithmic gain applying section 3 83 applies the logarithmic gain a2p to only a sample that is partially selected by sample extracting section 3 82 (a sample of the extraction flag SelectFlag(k=l). Logarithmic gain applying section 3 83 outputs the decoded spectrum S5'(k) to orthogonal transform processing section 356. In this case, a low frequency part (0