A code length of image coded data is length-fixed in accordance with a code length representing a required criterion. For this purpose, a discrete wavelet transformation unit 110 performs discrete wavelet transformation of image data. A factor quantization unit 112 performs quantization. An entropy coding unit 113 performs entropy coding of a factor quantized value by arithmetic coding. If the code length of quasi image coded data is longer than the code length designated by a designated image coded data code length inputting unit 102, entropy coded values are deleted in the unit of sub-bands so that the code length of the quasi image code data equals the designated code length. If the code length of quasi image coded data is shorter than the designated code length, adjustment bits are added.