1. A speech synthesis apparatus which generates synthesized speech corresponding to inputted text information, said apparatus comprising: an incomplete part-of-sentence detection unit operable to detect from among the text information a part-of-sentence which is linguistically incomplete because of a missing character string in the part-of-sentence; an incomplete part-of-sentence obscuring unit operable to reduce an acoustic clarity of the synthesized speech corresponding to the incomplete part-of-sentence detected by said incomplete part-of-sentence detection unit; a complementation unit operable to complement the detected incomplete part-of-sentence with a complement character string; and a speech synthesis unit operable to generate the synthesized speech based on the text information complemented by said complementation unit.