1. An image decoding apparatus comprising: an entropy decoding unit which obtains a first quantization parameter for a first plurality of macroblocks from a bitstream, where the first plurality of macroblocks are not located on a boundary of a region; an inverse-quantizing unit which calculates a second quantization parameter for a second plurality of macroblocks in a predefined manner, where the second plurality of macroblocks are located on the boundary of the region, and inverse-quantizes the first plurality of macroblocks using the first quantization parameter and the second plurality of macroblocks using the second quantization parameter, respectively; and an inverse-transform unit which inverse-transforms the inverse-quantized first plurality of macroblocks and second plurality of macroblocks.