An object of the present invention is to provide a device and a method for generating a synthesized speech that has an utterance form that matches music. A musical genre estimation unit of the speech synthesizing device estimates the musical genre to which a received music signal belongs, an utterance form selection unit references an utterance form information storage unit to determine an utterance form from the musical genre. A prosody generation unit references a prosody generation rule storage unit, selected from prosody generation rule storage units 151 to 15N according to the utterance form, and generates prosody information from a phonetic symbol sequence. A unit waveform selection unit references a unit waveform data storage unit, selected from unit waveform data storage units 161 to 16N according to the utterance form, and selects a unit waveform from the phonetic symbol sequence and the prosody information. A waveform generation unit generates a synthesized speech waveform from the prosody information and the unit waveform data.