The present invention relates to a moving image data compressing method that enables improvement of the efficiency of compressing moving images and reduction in the processing load due to JPEG 2000 system. In the compressing method, in sequentially compressing, according to JPEG 2000, image frames that are disposed along a time axis without compressing the image frames in the time axis direction, a process of detecting movement of image elements is performed prior to EBCOT, with one or more code blocks, each of which being a minimum processing unit of the EBCOT, as one detection unit. While EBCOT is performed for each of code blocks that constitute a detection unit on which movement has been detected, EBCOT is skipped and predetermined data is supplemented for each of code blocks that constitute a detection unit on which movement has not been detected. Thus, the number of times of processing by EBCOT with a large computation amount can be reduced.