1. An image decoding apparatus comprising: an entropy decoding unit which decodes image data including information on a value of a quantization parameter for each region in a bitstream obtained by encoding each region with a different quantization parameter value; and an inverse-quantizing unit which inverse-quantizes the decoded image data using determined values of the quantization parameters, the determined values of the quantization parameters obtained by determining a value of a quantization parameter for each region using the decoded information on the value of the quantization parameter for each region, so that image quality is lowered in a boundary of a region of interest and so that the determination of the value of the quantization parameter for each region is region specific.