An apparatus for synthesizing a voice signal using a plurality of phonetic piece data each indicating a phonetic piece which contains at least two phoneme sections corresponding to different phonemes, the apparatus comprising: a phonetic piece adjustment part that forms a target section from a first phonetic piece and a second phonetic piece so as to connect the first phonetic piece and the second phonetic piece to each other such that the target section is formed of a rear phoneme section of the first phonetic piece corresponding to a consonant phoneme and a front phoneme section of the second phonetic piece corresponding to the consonant phoneme, and that carries out an expansion process for expanding the target section by a target time length to form an adjustment section such that a central part of the target section is expanded at an expansion rate higher than that of a front part and a rear part of the target section, to thereby create synthesized phonetic piece data of the adjustment section having the target time length and corresponding to the consonant phoneme; and a voice synthesis part that creates a voice signal from the synthesized phonetic piece data created by the phonetic piece adjustment part, wherein the phonetic piece data comprises a plurality of unit data corresponding to a plurality of frames arranged on a time axis, wherein, in case that the target section corresponds to an unvoiced consonant phoneme, the phonetic piece adjustment part sequentially selects the unit data of each frame of the target section as unit data of each frame of the adjustment section to create the synthesized phonetic piece data, and wherein a velocity, at which each frame in the target section corresponding to each frame in the adjustment section is changed according to passage of time in the adjustment section, is decreased from a front part to a central point of the adjustment section and increased from the central point to a rear part of the adjustment section. a phonetic piece adjustment part that forms a target section from a first phonetic piece and a second phonetic piece so as to connect the first phonetic piece and the second phonetic piece to each other such that the target section is formed of a rear phoneme section of the first phonetic piece corresponding to a consonant phoneme and a front phoneme section of the second phonetic piece corresponding to the consonant phoneme, and that carries out an expansion process for expanding the target section by a target time length to form an adjustment section such that a central part of the target section is expanded at an expansion rate higher than that of a front part and a rear part of the target section, to thereby create synthesized phonetic piece data of the adjustment section having the target time length and corresponding to the consonant phoneme; and a voice synthesis part that creates a voice signal from the synthesized phonetic piece data created by the phonetic piece adjustment part, wherein the phonetic piece data comprises a plurality of unit data corresponding to a plurality of frames arranged on a time axis, wherein, in case that the target section corresponds to an unvoiced consonant phoneme, the phonetic piece adjustment part sequentially selects the unit data of each frame of the target section as unit data of each frame of the adjustment section to create the synthesized phonetic piece data, and wherein a velocity, at which each frame in the target section corresponding to each frame in the adjustment section is changed according to passage of time in the adjustment section, is decreased from a front part to a central point of the adjustment section and increased from the central point to a rear part of the adjustment section.