1. A speech information processing method comprising: a step of obtaining a duration of a predetermined unit of phonological series based on a duration model for an entire segment; a step of obtaining a duration of each or phonemes constructing said phonological series based on a duration model for a partial segment; a setting step of setting a duration of each of said phonemes based on said duration of the phonological series and said duration of each of said phonemes; and a speech synthesis step of synthesizing speech based on said duration of each of said phonemes set at said setting step.