1. A speech synthesis method comprising: a separating step of separating, from an input text, a singing data portion specified by a singing tag and the other text portion; a singing metrical data forming step of forming singing metrical data from said singing data; a speech symbol sequence forming step of forming a speech symbol sequence for said text portion; a metrical data forming step of forming metrical data from said speech symbol sequence; and a speech synthesis step of synthesizing the speech based on said singing metrical data or said metrical data.