An image coding method performs intra prediction with a higher coding efficiency by coding image data on a block-by-block basis. The method generates a predicted block by predicting a current block; computes a difference between the current block and the predicted block; codes the difference computed in the computing; decodes the difference coded in the coding; and adds the difference decoded in the decoding to the predicted block to generate a decoded block. The generating of the predicted block includes detecting an edge in a previously decoded block corresponding to a block adjacent to the current block; and extrapolating or interpolating previously decoded image data corresponding to a pixel included in the block adjacent to the current block, along a direction of the edge detected in the detecting to generate the predicted block.