1. A text-to-speech synthesizer for selecting necessary speech segment information from speech segment database based on reading and word class information on input text information and generating a speech signal based on the selected speech segment information, comprising: text analyzing means ( 12 ) for analyzing the input text information and obtaining reading and word class information; prosody generating means ( 13 ) for generating prosody information based on the reading and the word class information; plural speech instructing means ( 17 ) for instructing simultaneous speaking of an identical input text by a plurality of voices; and plural speech synthesizing means ( 16 ) for generating a plurality of synthesized speech signals based on prosody information from the prosody generating means ( 13 ) and speech segment information selected from the speech segment database ( 15 ) upon reception of an instruction from the plural speech instructing means ( 17 ).