A picture data compression coding device sets a normalizing coefficient which matches a block of picture data and normalizes the picture data by the normalizing coefficient, whereby an adequate compression ratio is selected on a block-by-block basis. The coding device sets a normalizing coefficient in response to the sum of activities of individual blocks and normalizes picture data by the normalizing coefficient, thereby maintaining the amount of coded data constant at all times. Further, the coding device normalizes picture data by multiplying them by a reciprocal of the normalizing coefficient so as to eliminate the need for a divider. A decoding device decodes the data having been coded by the coding device.