PURPOSE: To expand the decoding range of a code by adjusting a marker relevant value based on a marker corresponding value in a quantized value corresponding to the prescribed marker of a 1st code and a minimum value in a quantized value depending on the quantized width at a current sample point and corresponding to a 2nd code.

CONSTITUTION: A quantized value is read from a table ROM 16 by a code sent from a code deciding section 12 and a quantized width sent from a quantization width updating section 13 and outputted to an adder 17. The adder 17 calculates the sum of outputs of a primary decoding section 14, a secondary decoding section 15 and a prediction section 18 to output a synthesized voice signal. That is, a marker corresponding value in a quantized value corresponding to the prescribed marker of the 1st code and a minimum value in a quantized value depending on the quantized width at a current sample point and corresponding to the 2nd code are added, a difference between the sum and the maximum value of the quantized value of the 1st code except the marker corresponding value is calculated, and the marker corresponding value is adjusted so that the calculated difference is equal to the quantized width at the current sample point. Thus, the decoding range is expanded.