13. A speech synthesis method for a speech synthesis device, the method comprising: performing language processing of input text; selecting a central segment from among a plurality of speech segments based on the language processing result; generating prosody information based on the selected central segment; selecting a non-central segment based on the central segment and the generated prosody information; and generating a synthesized speech waveform based on the central segment, and the non-central segment, wherein generating prosody information of the non-central segment is based on the prosody information of the central segment and the language processing result.
13. A speech synthesis method for a speech synthesis device, the method comprising: performing language processing of input text; selecting a central segment from among a plurality of speech segments based on the language processing result; generating prosody information based on the selected central segment; selecting a non-central segment based on the central segment and the generated prosody information; and generating a synthesized speech waveform based on the central segment, and the non-central segment, wherein generating prosody information of the non-central segment is based on the prosody information of the central segment and the language processing result. 15. The speech synthesis method according to claim 13 , wherein said selecting the central segment selects a speech segment having the longest segment length as a central segment.