A speech information processing apparatus which sets the duration of phonological series with accuracy, and sets a natural phoneme duration in accordance with phonemic/linguistic environment. For this purpose, the duration of a predetermined unit of phonological series is obtained based on a duration model for an entire segment. Then, duration of each of phonemes constructing the phonological series is obtained based on a duration model for a partial segment. Then, duration of each phoneme is set based on the duration of the phonological series and the duration of each phoneme.