PURPOSE: To implement information quantity control and picture quality improvement by assigning a coding bit number to each block being a component of one pattern according to an inter-pattern distortion for each block and coding the result.

CONSTITUTION: A picture signal for one pattern is converted into the scanning in the unit of blocks by a block scan circuit 1 and a picture data of a preceding frame being an output of a frame memory 10 is subtracted from a picture data delayed by a 1-frame delay circuit 2 in the unit of a block at a subtractor 3. An inter-frame differential data is quantized by a quantizer 5 through a DCT transformation device 4. Then a coded data is generated by a variable length coding circuit 6. In this case, the coded data is generated by a variable length coding circuit 6. In this case, an inverse quantizer T and an inverse DCT transformation device 8 apply decoding processing to the signal after quantization at the coder side and a picture data of a preceding frame being an output of the frame memory 10 is added to the inter-frame differential data by an adder 9 and the result is stored in the frame memory 10.