An inverse wavelet transformer causes a level-graded buffer to store one of two lines of coefficient data generated through a synthesis filtering operation. In order to adjust an output timing of image data, the inverse wavelet transformer causes an output buffer to store temporarily the other line of the two lines of coefficient data in a period throughout which the output buffer stores no baseband image data and then causes the level-graded buffer to store the other line of the two lines of coefficient data. In this way, the level-graded buffer stores coefficients generated through the synthesis filtering operation on a line-by-line basis.