24. A speech synthesis apparatus comprising: a dividing unit configured to divide an input text into language units; an estimation unit configured to estimate a punctuation mark incidence at a boundary between language units in the input text, the punctuation mark incidence indicating a degree that a punctuation mark occurs at the boundary, based on attribute information items of a plurality of language units adjacent to the boundary; a determination unit configured to determine a type of a prosodic boundary between the language units based on the punctuation mark incidence between the language units estimated; a selecting unit configured to select a prosodic control rule for speech synthesis based on the type of the prosodic boundary between the language units determined; and a synthesizing unit configured to synthesize a speech corresponding to the input text using the prosodic control rule selected.
26. The speech synthesis apparatus according to claim 24 , further comprising: a second memory to store a plurality of prosodic control rules for speech synthesis each including a condition for a type of the prosodic boundary between the language units; and wherein the selecting unit selects, from the prosodic control rules for speech synthesis, the prosodic control rule whose condition meets the type determined.