To improve the inter-frame prediction performance of spectral coeffts. and to improve the spectral coefft. quantization performance, by executing spectral coefft. quantization by taking the correlation of the spectral coefft. change existing between respective bands into consideration.

A signal dividing circuit 3 calculates the voice signals of the respective bands by executing predetermined frequency band division. Analyzing circuits 5, 7 calculate spectral coefft. spectra in the respective bands. Adder circuits 15, 17 obtain predicted residual vectors by subtracting the predicted coefft. vectors of the respective bands calculated by a dividing circuit 13 from the spectral coefft. vectors. Adder circuits 8, 18 output the quantization spectral coefft. vectors from output terminals 21 and 22 by adding the predicted coefft. vectors calculated to quantization predicted residual vectors by an optimum prediction circuit 11. This optimum prediction circuit 11 calculates the predicated coefft. vectors of the entire band by using the quantization value vectors of the entire band received from a coefft. quantization circuit 19 and the coefft vectors of the entire band.