Abstract: The encoder unit of the vocoder device includes the AR code-book, the MA code-book, and the voice source code-book storing code words each corresponding to a set of the AR, the MA, and the voice source parameters, respectively, which are obtained beforehand by means of the "analysis by synthesis" of a multitude of speech waveform examples and then clustering the resulting respective parameters. The AR preliminary selector, the MA preliminary selector, and the voice source preliminary selector select from respective code-books a predetermined finite number of code words approximating the input speech signal, and in synchronism with the voice source position detected by the voice source position detector the speech synthesizer synthesizes a number of synthesized speech waveforms corresponding to the combinations of the selected AR, MA, and voice source parameters.