A strained-rough-voice conversion unit (10) is included in a voice conversion device that can generate a “strained rough” voice produced in a part of a speech when speaking forcefully with excitement, nervousness, anger, or emphasis and thereby richly express vocal expression such as anger, excitement, or an animated or lively way of speaking, using voice quality change. The strained-rough-voice conversion unit (10) includes: a strained phoneme position designation unit (11) designating a phoneme to be uttered as a “strained rough” voice in a speech; and an amplitude modulation unit (14) performing modulation including periodic amplitude fluctuation on a speech waveform. The amplitude modulation unit (14) generates, according to the designation of the strained phoneme position designation unit (11), the “strained rough” voice by performing the modulation including periodic amplitude fluctuation on the part to be uttered as the “strained rough” voice, in order to generate a speech having realistic and rich expression uttering forcefully with excitement, nervousness, anger, or emphasis.