PURPOSE: To obtain a quantizer not needing a special adaptor for an inverse quantizer and able to be coded efficiently at an optional rate.

CONSTITUTION: A quantization error calculator 10 calculates a quantization error 11 when an input signal 1 is quantized. A code length calculator 12 quantizes an input signal 1 and also calculates a code length 13 in the case of coding. A same code is allocated to the same quantization in each quantization means. A set of the quantization error 11 and the code length 13 of each quantization means are selected by a selector 20 and the quantization with a small code length and a small quantization error is selected. The selected quantization means is informed to a quantizer 2 by a selection signal 21 and the quantizer 2 quantizes the input signal 11 to an output a quantized value 3.