PURPOSE: To remove the polarization of the quantization error, by repeating plural times the quantization operation of the difference of the vector, thinking the forecasting error signal as a vector summarizing the plural signals.

CONSTITUTION: The switch SWA, first, is connected to the connecting point a1 side, initial value is obtained and after that, the switch is connected to the connecting point a2. The forecasting error vector signal →E is obtained by subtracting by the subtractor 12 the predictor made by the forecasting device 14 from the input vector signal converted to the input vector signal summarizing the plural samples. Further, the signal →E is quantized by the quantizing device, the vector quantization output is obtained and the signal is inputted to the forecasting device 14 by adding the output and the predictor of the forecasting device 14 by the adder 15. The transfer quantization is executed by repeating the above- mentioned forecasting and quantization plural times. And, after the transfer frequency of (n) times ends, the switch SWA is connected to the connecting point a2 side and the final quantization output is sent to the communication channel encoder.