In a speech synthesizer apparatus, a weighting coefficient training controller calculates acoustic distances in second acoustic feature parameters between one target phoneme from the same phoneme and the phoneme candidates other than the target phoneme based on first acoustic feature parameters and prosodic feature parameters, and determines weighting coefficient vectors for respective target phonemes defining degrees of contribution to the second acoustic feature parameters for respective phoneme candidates by executing a predetermined statistical analysis therefor. Then, a speech unit selector searches for a combination of phoneme candidates which correspond to a phoneme sequence of an input sentence and which minimizes a cost including a target cost representing approximate costs between a target phoneme and the phoneme candidates and a concatenation cost representing approximate costs between two phoneme candidates to be adjacently concatenated, and outputs index information on the searched out combination of phoneme candidates. Further, a speech synthesizer synthesizes a speech signal corresponding to the input phoneme sequence by sequentially reading out speech segments of speech waveform signals corresponding to the index information and concatenating the read speech segments of the speech waveform signals.