1. A voice quality change portion locating apparatus which locates, based on language analysis information regarding a text, a portion of the text where voice quality may change when the text is read aloud, said apparatus comprising: a storage unit in which a rule is stored, the rule being used for judging likelihood of the voice quality change based on phoneme information and prosody information; a voice quality change estimation unit operable to estimate the likelihood of the voice quality change which occurs when the text is read aloud, for each predetermined unit of an input symbol sequence including at least one phonologic sequence, based on (i-1) phoneme information and (i-2) prosody information which are included in the language analysis information that is a symbol sequence of a result of language analysis including a phonologic sequence corresponding to the text, and (ii) the rule; and a voice quality change portion locating unit operable to locate a portion of the text where the voice quality change is likely to occur, based on the language analysis information and a result of the estimation performed by said voice quality change estimation unit.
13. The voice quality change portion locating apparatus according to claim 1 , further comprising: a voice recognition unit operable to recognize voice by which a user reads the text aloud; a voice analysis unit operable to analyze an occurrence degree of the voice quality change, for each predetermined unit which includes each phoneme unit of the voice of the user, based on a result of the recognition performed by said voice recognition unit; and a text evaluation unit operable to compare (i) the portion of the text which is located by said voice quality change locating unit as where the voice quality change is likely to occur to (ii) a portion where the voice quality change has actually occurred in the voice of the user, based on (a) the portion of the text where the voice quality change is likely to occur and (b) a result of the analysis performed by said voice analysis unit.