Provided is an image decoding apparatus that restores a quantized transform block by inversely scanning 1D quantized coefficients, inversely quantizes the quantized transform block using a quantization step size, inversely transforms the transform block to generate a residual block, and generates a prediction block according to an intra prediction mode. When a size of the transform block is 8×8, the quantized transform block is divided into a plurality of sub-blocks, and the plurality of sub-blocks and coefficients of each sub-block are scanned using a same scan pattern determined according to the intra prediction mode. When the intra prediction mode is a horizontal mode, the scan pattern is a vertical scan.