Provided is an image decoding apparatus that receives an intra prediction mode and one-dimensional (1D) quantized coefficients, restores a quantized transform block by inversely scanning the 1D quantized coefficients, inversely quantizes the quantized transform block using a quantization step size to generate a transform block, inversely transforms the transform block to generate a residual block, and generates a prediction block according to the 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.