An image decoding apparatus for receiving encoded image information from an external source and decoding encoded image data, included in the encoded image information, to image data, the apparatus comprising: storage means for storing the encoded image information and image data corresponding to a first raster (#N) or column; first decoding means configured to receive, from said storage means, first encoded image data corresponding to a second raster (#(N+1)) or column, successive to the first raster (#N) or column, from the encoded image information stored in said storage means and configured to receive, from said storage means, as first reference data, the image data corresponding to the first raster (#N) or column, and configured to decode the first encoded image data to first image data based on the first reference data; a buffer configured to temporarily store the first image data decoded by said first decoding means; second decoding means configured to receive, from said buffer, the first image data as second reference data, and configured to receive, from said storage means, second encoded image data corresponding to a third raster (#(N+2)) or column, successive to the second raster (#(N+1)) or column, from the encoded image information stored in said storage means, and configured to decode the second encoded image data, received from said storage means, based on the second reference data; and decoding control means operable to control said first decoding means and said second decoding means to repetitively execute decoding of such first encoded image data by said first decoding means and decoding of such second encoded image data by said second decoding means in parallel, wherein the first image data decoded by the first decoding means is outputted to both of the buffer and the storage means, and the second image data which is decoded by the second decoding means based on the first image data outputted to the buffer, is outputted to the storage means. storage means for storing the encoded image information and image data corresponding to a first raster (#N) or column; first decoding means configured to receive, from said storage means, first encoded image data corresponding to a second raster (#(N+1)) or column, successive to the first raster (#N) or column, from the encoded image information stored in said storage means and configured to receive, from said storage means, as first reference data, the image data corresponding to the first raster (#N) or column, and configured to decode the first encoded image data to first image data based on the first reference data; a buffer configured to temporarily store the first image data decoded by said first decoding means; second decoding means configured to receive, from said buffer, the first image data as second reference data, and configured to receive, from said storage means, second encoded image data corresponding to a third raster (#(N+2)) or column, successive to the second raster (#(N+1)) or column, from the encoded image information stored in said storage means, and configured to decode the second encoded image data, received from said storage means, based on the second reference data; and decoding control means operable to control said first decoding means and said second decoding means to repetitively execute decoding of such first encoded image data by said first decoding means and decoding of such second encoded image data by said second decoding means in parallel, wherein the first image data decoded by the first decoding means is outputted to both of the buffer and the storage means, and the second image data which is decoded by the second decoding means based on the first image data outputted to the buffer, is outputted to the storage means.