1. A speech recognition synthesis based encoding/decoding method comprising the steps of: recognizing character information from an input speech signal; detecting first prosody information from said input speech signal; encoding said character information and said first prosody information to acquire code data; transferring or storing the code data; decoding said transferred or stored code data to said character information and said first prosody information; selecting a synthesis unit codebook from a plurality of synthesis unit codebooks in accordance with one of said first prosody information and a specified type of a synthesized speech, the plurality of synthesis unit codebooks storing second prosody information prepared from speech data of different speakers, the selecting step including computing error between the first prosody information and the second prosody information and selecting from said synthesis unit codebooks a synthesis unit codebook which minimizes the error; and synthesizing a speech signal using said character information and the selected said synthesis unit codebook.