An excitation vector generator comprises a pulse vector generating section having N channels (N≧1) for generating pulse vectors, a storing section for storing M (M≧1)kinds of dispersion patterns every channel in accordance with N channels, a selecting section for selectively taking out a dispersion pattern from the storing section every channel, a dispersion section for performing a superimposing calculation of the extracted dispersion pattern and the generated pulse vectors every channel so as to generate N dispersion vectors, excitation vector generating section for generating an excitation vector from N dispersion vectors generated.