PURPOSE: To suppress the generation of an excessive amount of codes and obtain compressibility which is efficient by finding a still area from the mean and variance of predictive error signals and neglecting the coding of the high frequency component of orthogonal transformation coefficients in a block in the found area.

CONSTITUTION: A mean and variance calculation part 12 calculates a mean value and a variance value and an encoding coefficient selection part 13 generates an encoding select signal for selecting a coefficient to be encoded and a coefficient not to be encoded in the block from the mean value and variance value. A high-frequency component removal part 14 substitutes zero for orthogonal transformation coefficients, which are rearranged in frequency order by a coefficient rearrangement part 10, unless the coefficients are encoded with the encoding select signal. Orthogonal transformation quantization coefficients are encoded at a variable length encoding part 15 on a variable length basis and written in a transmitting buffer memory part 16. The encoded data written in the memory part 16 are sent out of an output terminal 21 with a certain electric transmission rate.