1. A speech synthesizing apparatus for synthesizing a speech signal corresponding to a text, comprising: behavior-state changing means for changing a behavior state according to a behavior model; emotion-state changing means for changing an emotion state according to an emotion model; selecting means for selecting control information according to at least one of the behavior state and the emotion state; and synthesizing means for synthesizing a speech signal corresponding to the text according to speech synthesizing information included in the control information selected by the selecting means.