PURPOSE: To improve the efficiency of encoding by sectioning an input forecasting error signal into adequate blocks and performing block-by-block encoding adaptively.

CONSTITUTION: A picture signal is converted by an A/D converter 1 into a digital picture signal, which is supplied to the subtracter 4 and forecasting device 3 of forecasting encoder 2. The forecasting error signal from the forecasting encoder 2 is supplied to the delay circuit 6 and characteristic discriminating circuit 7 of an unequal-length encoder 5. The characteristic discriminating circuit 7 sections the input forecasting error signal into proper blocks to discriminate on which characteristics of the frequency distribution of three kind of forecasting error signals every block of the input signal is close to, and a mode signal for showing the discrinated characteristic is outputted to a code converter 8. The delay circuit 6 delays the forecasting error signal corresponding to the necessary time of a discrimination on the characteristic of the input signal by the circuit 7 and the output of the circuit 6 is supplied to the code converter 8.