1. A moving picture encoding apparatus comprising: predicted image generating means for generating a predicted image, with respect to a target image as an object to be encoded among a plurality of images constituting a moving picture; difference image generating means for executing a difference operation between the target image and the predicted image to generate a difference image; encoding means for encoding the difference image to generate an encoded difference signal; decoding means for decoding the encoded difference signal to generate a decoded difference image; reproduced image generating means for executing a sum operation of the decoded difference image and the predicted image to generate a reproduced image; storing means for storing a reference image to be used by the predicted image generating means in order to generate the predicted image; and image updating means for performing a weighted summation of a first image which is one of the reproduced image and the reference image stored in the storing means, and at least a portion of a second image which is the other of the reproduced image and the reference image, to generate an updated image, wherein the image updating means stores the updated image into the storing means, and wherein the predicted image generating means uses the updated image stored in the storing means, as a reference image for generating a predicted image with respect to another target image.