1. A speech enhancement apparatus that corrects and outputs unclear portions of input speech data, the speech enhancement apparatus comprising: a waveform-feature-quantity calculating unit that calculates a waveform feature quantity of the speech data for each phoneme, the speech data being input along with phoneme boundary data that splits the speech data into phonemes; a correction determining unit that determines a necessity of correction of the speech data for each phoneme, based on the waveform feature quantity calculated by the waveform-feature-quantity calculating unit; and a waveform correcting unit that corrects the speech data, the necessity of correction thereof is determined by the correction determining unit, for each phoneme by using waveform data that is prior stored in a phonemewise-waveform-data storage unit.