A decoding method decodes a bit stream in an image decoding apparatus. The method includes receiving a weight parameter that is added to a luma quantization parameter as the bit stream. The method also includes decoding, in a decoding unit in the image decoding apparatus, the bit stream, and generating a luma component of quantized coefficients and a chroma component of quantized coefficients. Further, the method includes performing, in a dequantization unit in the image decoding apparatus, dequantization on the luma component of quantized coefficients using the luma quantization parameter and the chroma component of quantized coefficients using a chroma quantization parameter calculated on the basis of the luma quantization parameter weighted by an add operation of the weight parameter. In addition, the method includes performing, in a transform unit in the image decoding apparatus, an inverse orthogonal transform.