An image encoding apparatus is provided, including a lossless compression unit that performs lossless compression on deblocked data on a window basis during encoding of image data; a lossless compression controller that determines a relation between the deblocked data and the losslessly compressed deblocked data and determines a size of the window; a cache controller that selects losslessly compressed deblocked data corresponding to reference data used for motion compensation or motion estimation from the losslessly compressed deblocked data, based on the relation between the deblocked data and losslessly compressed deblocked data; a lossless compression reconstruction unit that decodes the selected losslessly compressed deblocked data to reconstruct the reference data; and a cache storage unit that stores the reconstructed reference data.