1. A speech synthesizing apparatus comprising: a storage unit that stores speech segments; and a segment selection unit that selects a segment suited to a target segment environment from among a plurality of candidate segments selected from the storage unit, wherein the segment selection unit performs control to exclude, from the candidate segment which is a candidate of the selection, a segment having a prosody change amount less than a selection criterion that is determined based on a prosody change amount of the candidate segments.
1. A speech synthesizing apparatus comprising: a storage unit that stores speech segments; and a segment selection unit that selects a segment suited to a target segment environment from among a plurality of candidate segments selected from the storage unit, wherein the segment selection unit performs control to exclude, from the candidate segment which is a candidate of the selection, a segment having a prosody change amount less than a selection criterion that is determined based on a prosody change amount of the candidate segments. 17. The speech synthesizing apparatus according to claim 1 , further comprising, in addition to the segment selection unit: a language processing unit that generates a language processing result including a symbol sequence representing a of synthesized speech generated based on the language processing reading from text, and morphological part of speech, conjugation, and accent information; a prosody generation unit that generates prosody information result; a prosody control unit that generates a waveform having a prosody generated by the prosody generation unit, from speech segments selected by the segment selection unit; a waveform connection unit that concatenates speech segments output by the prosody control unit, to output the result as synthesized speech; and a speech segment information storage unit that stores speech segments divided into synthesis units and attribute information of each speech segment; wherein the segment selection unit comprises: a unit cost calculation unit that receives the language processing result generated by the language processing unit, and the prosody information generated by the prosody generation unit, generates the target segment environment for each synthesis unit, selects, as candidate segments, a plurality of speech segments matching information designated by the target segment environment, from the speech segment information storage unit, and, calculates a unit cost of each candidate segment, based on a segment environment of the candidate segments and the target segment environment; a concatenation cost calculation unit that calculates concatenation cost of each of the candidate segments, based on information of each of the candidate segments, and attribute information of each speech segment from the speech segment information storage unit; a candidate selection unit that narrows down candidate segments, based on information of each of the candidate segments, the unit cost and the concatenation cost, and outputs information of the narrowed-down and selected candidate segments and unit cost thereof; an optimum segment search unit that obtains, based on information of the candidate segments, the unit cost, and the concatenation cost, an optimum segment sequence, which is a speech segment sequence in which an objective function related to the unit cost and the concatenation cost is optimized, to be provided to the prosody control unit; a prosody change amount calculation unit that calculates prosody change amount of optimum segments in question, based on each segment of the optimum segment sequence output from the optimum segment search unit, the prosody information from the prosody generation unit, and attribute information of the optimum segments from the speech segment information storage unit; a selection criterion calculation unit that calculates a selection criterion necessary for distinguishing existence of a segment whose prosody change amount is particularly small in comparison to others, based on prosody change amount of each optimum segment from the prosody change amount calculation unit; and a decision unit that decides whether or not there exists a segment whose prosody change amount is particularly small in comparison to others, based on optimum segments from the optimum segment search unit, prosody change amount of each segment from the prosody change amount calculation unit, and a selection criterion supplied from the selection criterion calculation unit, in a case where it is decided that there exists a segment whose prosody change amount is particularly small in comparison to others, supplies a segment whose prosody change amount is particularly small to the candidate selection unit, the candidate selection unit re-executing search of candidate segments, and in a case where it is decided that there does not exist a segment whose prosody change amount is particularly small in comparison to others, or in a case where the number of times the search is repeated exceeds an upper limit, and supplies optimum segments to the prosody control unit; wherein the candidate selection unit excludes, a segment supplied from the decision unit, from among the candidate segments supplied from the concatenation cost calculation unit, and supplies a candidate segment that is not excluded, and unit cost and concatenation cost of the candidate segment to the optimum segment search unit.