The picture decoding method according to the present invention is a decoding method for decoding coded pictures by inverse quantization (IQ1) and inverse orthogonal transformation, in which a quantization matrix which defines a scaling ratio of a quantization step for each component is multiplied by a multiplier (IQ11), which is a coefficient for frequency transformation or a quantization step, and also, a result of the multiplication is multiplied by a quantized value, as a process of inverse quantization.