An image processing device including a decoding section that decodes an encoded stream and generates quantized transform coefficient data, and an inverse quantization section that, taking transform coefficient data as transform units to be used during inverse orthogonal transform, inversely quantizes the quantized transform coefficient data decoded by the decoding section, such that in a case where a non-square transform unit is selected, the inverse quantization section uses a non-square quantization matrix, corresponding to a non-square transform unit, that is generated from a square quantization matrix corresponding to a square transform unit.