It is an object of the present invention to prevent an image distortion from occurring by using a line memory of small memory capacity. For example, an image is decomposed into strip regions 12, and each strip region 12 is filtered together with certain excess data 14 from a neighboring strip region 12 to prevent an image distortion from occurring at the boundary between the strip regions 12 while executing band decomposition on the strip region 12 which is smaller in size than the entire image with a smaller line memory. In the band decomposition, a line memory which supports band decomposition of, for example, 3 decomposition levels is repeatedly and recursively used, whereby band decomposition of deeper decomposition levels is executed without any problems. In this manner, line-based wavelet transform for deeper decomposition levels is executed with a small line memory. Also reverse wavelet transform is executed in the similar manner.