1. An image reproducing method of decoding a moving picture stream having been subjected to inter-picture prediction encoding with a reference image memory accessed, the method comprising: performing first decoding for decoding the moving picture stream on a picture-by-picture basis to estimate traffic to the reference image memory on the picture-by-picture basis; and performing second decoding for decoding the moving picture stream on the picture-by-picture basis to generate a reproduction image, wherein in the second decoding, where a picture to be decoded is to be stored as a reference image in the reference image memory after being decoded, a compression mode in storing the picture to be decoded in the reference image memory is determined based on the traffic for a picture referring to the picture to be decoded, which has been estimated in the first decoding.