This invention relates to a coding method for motion-image data and others effective in a special interactive environment for transmitting motion-image data with information concentrated on only a partial region of a display image as in a two-way interactive system implementing real-time two-way interaction. The coding method involves dividing an image frame forming motion-image data into a plurality of rectangular regions, and grouping each of these rectangular regions into a preset ROI and a non-ROI. These rectangular regions are sequentially compressed so that a code length of a rectangular region grouped into the ROI is larger than a code length of a rectangular region grouped into the non-ROI, thereby generating coded data of each image frame.