Provided are an image encoding apparatus and an image decoding apparatus. The image encoding apparatus includes a compression unit compressing a reference image by reducing a resolution of the reference image in a resolution adjustment mode determined from among at least two resolution adjustment modes according to a distribution of values of pixels of the reference image, and providing the compressed reference image to a memory, a reconstruction unit reconstructing the reference image by increasing a resolution of the compressed reference image stored in the memory to an original resolution, a predictive encoding unit performing predictive encoding on a current image by using the reconstructed reference image, and a predictive decoding unit generating the reference image by performing decoding on the predictive encoded current image, and providing the generated reference image to the compression unit.