1. An image predictive coding method for coding a target image by obtaining a predictive image from a reference image including an object image comprising a luminance signal indicating a pixel value and a shape signal indicating whether a pixel is located inside or outside the object image, said method comprising: dividing the target image into a plurality of target subareas; obtaining a substitute pixel value for a pixel located outside the object image, which is determined according to the shape signal, in a subarea of the reference image by using a pixel value of a pixel located inside the object image, which is determined according to the shape signal, in the subarea of the reference image; generating a padded predictive subarea by padding the pixel located outside the object image with the substitute pixel value; and obtaining and coding a pixel value difference between the target subarea and the padded predictive subarea.