1. A vector quantization apparatus for performing coding of a target vector by multi-stage vector quantization, the apparatus comprising: a predictor for generating a predictive error vector based on the target vector; a first codebook for storing a plurality of first code vectors; a first quantizer for performing a first distance calculation using the predictive error vector provided by the predictor, a first code vector of the plurality of first code vectors stored in the first codebook and the target vector, and performing a first stage of the coding of the target vector using a result of the first distance calculation; an amplifier storage for storing a plurality of scalars associated with codes of the plurality of first code vectors, respectively, each of the plurality of scalars being obtained by pre-training wherein the pre-training encodes a plurality of speech data by using one of the first code vectors associated with each of the codes and minimizes a sum of encoded distortions of the encoded plurality of speech data; and a second quantizer for determining a third code vector by multiplying a second code vector stored in a second codebook and one of the plurality of scalars associated with a code of the first code vector determined at the first stage of coding together, calculating a difference vector between the target vector and the first code vector, performing a second distance calculation using the predictive error vector provided by the predictor, the difference vector, and the third code vector, and performing a second stage of the coding of the target vector using a result of the second distance calculation.