PURPOSE: To attain the reduction in average distortion by scaler quantization with the same information amount by executing a two-stage quantization method using a specific vector dictionary.

CONSTITUTION: The vector quantizing section 21 decides to which an input vector belongs. When the input vector S belongs to a group 25a of a center of gravity point C1, a dispersion vector of the group 25a is represented by a barycentric vector representing the C1, and a coordinate with minimized distortion is selected from a lattice point 26 independent of each coordinate expressed by (B-B0) formed by using the dispersion vector. In this case, B-B0=4 and 16 lattice points 26 in total by 2-bit per coordinates x1, x2 are provided around the center of gravity C1. The number of the group 25 is transmitted by using B0 bits and the number of the lattice point 26 is transmitted from terminals 27, 28 to the decoder 13 as an output of the coder 11 by using (B-B0) bits. Thus, the two-stage quantization using 2B0×2 sets (B0<B, where B is the quantized bit number) of vector dictionaries is executed, the average distortion is made less than the scale quantization by using the same amount of information.