A data processor is provided to compression-code moving picture data without decreasing coding efficiency even if the moving picture includes a picture with particularly violent motion. The moving picture is obtained by presenting a plurality of frame pictures, each consisting of two field pictures, one after another. The processor (100) includes a memory (101) for storing the moving picture data, a calculating section (108) for calculating a parameter, representing how much the moving picture has changed, based on the moving picture data of the two field pictures, a determining section (109) for determining, by the parameter calculated, on what picture unit the moving picture data is going to be compression-coded by the intra-picture coding method and the forward predictive coding method and adopting a picture structure defining the predetermined picture unit, and a processing section (102-107, 110) for compression-coding the moving picture data, stored in the memory, according to the picture structure adopted, thereby generating compressed data.