A method for synthesizing a natural-sounding singing voice divides performance data into a transition part and a long sound part. The transition part is represented by articulation (phonemic chain) data that is read from an articulation template database and is outputted without modification. For the long sound part, a new characteristic parameter is generated by linearly interpolating characteristic parameters of the transition parts positioned before and after the long sound part and adding thereto a changing component of stationary data that is read from a constant part (stationary) template database. An associated apparatus for carrying out the singing voice synthesizing method includes a phoneme database for storing articulation data for the transition part and stationary data for the long sound part, a first device for outputting the articulation data, and a second device for outputting the newly-generated characteristic parameter of the long sound part.