A sound synthesizing apparatus includes a processor coupled to a memory. The processor configured to execute computer-executable units comprising: an information acquirer adapted to acquire synthesis information which specifies a duration and an utterance content for each unit sound; a prolongation setter adapted to set whether prolongation is permitted or inhibited for each of a plurality of phonemes corresponding to the utterance content of the each unit sound; and a sound synthesizer adapted to generate a synthesized sound corresponding to the synthesis information by connecting a plurality of sound fragments corresponding to the utterance content of the each unit sound. The sound synthesizer prolongs a sound fragment corresponding to the phoneme the prolongation of which is permitted in accordance with the duration of the unit sound.