An object of the present invention is to improve visual picture quality. A picture signal is divided into a plurality of macro blocks and coding is conducted in macro block units. The coding is conducted including quantization process by a quantization portion. A motion compensation portion outputs the quantity of motion, L, in macro block units. An average quantity of motion, L.sub.ave, of a reference picture stored in a frame memory is outputted from a division portion. A control portion compares the quantity of motion L with two reference values relative to the average quantity of motion L.sub.ave and makes a correction to lower the quantization step in the quantization portion for macro blocks whose quantity of motion L is between the reference values. Accordingly, picture quality is improved in part of picture where motion is small and deterioration of visual picture quality is noticeable. At the same time, since the correction is not applied to picture with such slow motion that deterioration of picture quality is small, redundancy of coded signal does not unnecessarily increase.