PROBLEM TO BE SOLVED: To generate various synthesized sounds differing in vocal quality from an existing sound.SOLUTION: A variable setting unit 52 causes a mixture ratio R to change with the passage of time in accordance with an instruction from a user. A fragment mixing unit 62 sequentially mixes each unit data in accordance with the mixture ratio R set by the variable setting unit 52 between fragment data PA including a plurality of unit data representing each unit interval of a sound fragment of a first sound and second fragment data PB including a plurality of unit data representing each unit interval of a sound fragment of a second sound. With regard to a steady period in which one phoneme of the phonemes to be synthesized is steadily continued, the fragment mixing unit 62 sequentially mixes each unit data corresponding to the phoneme in each of the fragment data PA and the fragment data PB in accordance with the mixture ratio R changing with the passage of time within a steady period H. A synthesis pro
