An image coding and decoding system is provided that includes an image coding apparatus and an image decoding apparatus. The image coding apparatus includes a coder that codes an input image, a first decoder that decodes the coded image to obtain a first reconstructed image, a first pixel difference value obtainer, a first average deriver, a first threshold value setter, a first comparator, and a first remover that removes a coding distortion. The image decoding apparatus includes an obtainer that obtains the first quantization parameter of the first block and the second quantization parameter of the second block, a second decoder that decodes the coded image, a second pixel difference value obtainer, a second average deriver, a second comparator, and a second remover that removes a coding distortion in an area disposed on both sides of a block boundary between the first block and the second block.