PURPOSE: To obtain a forecasting encoder of nonrecursive type in which a picture signal can be encoded and decoded with a prescribed bit rate, by providing a pre-processing circuit such as band limit circuit, quantization circuit and thinved-out control circuit.

CONSTITUTION: A picture signal inputted to an input terminal 1 is converted into a digital signal at an A/D converter 2 and quantized at a quantizing circuit 4. In this case, a control circuit 11 selects the quantizing characteristics with minute accuracy when the amount of information of a buffer memory 10 is less, and selects a coarse quantizing characteristic when that of the memory 10 is much. A forecasting device 6 outputs a forecasting signal, which is converted into a forecast error signal at a subtractor 7 and transmitted to a transmission line via an unequal length coding circuit 9. A decoder 14 stores the information to a buffer memory 16, performs inverting coding conversion corresponding to the code converting characteristics provided for the circuit 9 at an unequal length decoding circuit 17, and obtains a quantized forecast error signal, which is summed with the forecasting signal from a forecasting device 21 to be a decoding signal.