an image decoding device is provided which includes an intra prediction module for reconstructing an intra prediction mode and creating a prediction block of a current block or a sub block , an inverse scanning module for converting residual signals into a quantization block , an inverse quantization module for inversely quantizing the quantization block , and an inverse transform module for inversely - transforming the inversely - quantized block . a quantization parameter predictor for deriving the quantization parameter is created using quantization parameters of a left coding unit and a top coding unit of a current coding unit . therefore , it is possible to improve image quality by adaptively adjusting a quantization parameter of a current block depending on the size of a coding unit and enhance compression efficiency of an image by effectively encoding / decoding the quantization parameter to reduce the number of bits required for transmitting the quantization parameter .