A singing sound-synthesizing apparatus sequentially synthesizes vocal sounds based on singing data including lyric data of a lyric formed of a plurality of phonemes and sounding data designating a sounding time period over which the lyric data is sounded. A designating device designates a predetermined voiced phoneme from the plurality of phonemes of the lyric data. A sounding control device carries out sounding control such that sounding of the predetermined voiced phoneme designated by the designating device is started within the sounding time period designated for the plurality of phonemes by the sounding data and continued until the sounding time period designated for the plurality of phonemes elapses. In another form, ones of phoneme parameter sets and ones of coarticulation parameter sets corresponding to signing data are read from a phoneme data storing the phoneme parameter sets and the coarticulation parameter sets. A control signal is selectively supplied to at least one of a formant-synthesizing tone generator device that synthesizes formants of phonemes to be sounded to generate vocal sounds and a PCM tone generator device that generates vocal sounds by pulse code modulation, the PCM tone generator device having a waveform memory storing waveforms of unvoiced consonants, based on the corresponding ones of the phoneme parameter sets and the corresponding ones of the coarticulation parameter sets read from the phoneme data base to cause the at least one of the formant-synthesizing tone generator device and the PCM tone generator device to generate a vocal sound.