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