A singing voice synthesizing method synthesizes the singing voice by exploiting performance data, such as MIDI data. The input performance data are analyzed as the musical information including the pitch and the length of the sounds and the lyric (S2 and S3). If the musical information analyzed lacks in the lyric information, an arbitrary lyric is donated to an arbitrary string of notes (S9, S11, S12 and S15). The singing voice is generated based on the so donated lyric (S17).