Natural images which are similar to each other contained in a page represented by page description data are corrected so that they have natural appearance to the eye. To achieve this object, an image recognizing unit recognizes images in a page represented by page description data, and a natural image determining unit determines whether or not each recognized image is a natural image. An image analyzing unit calculates a setup condition for image correction for each natural image. A second correction condition calculating unit calculates, for the similar natural images being similar to each other, a correction condition for making image qualities of the similar natural images substantially uniform. An image correcting unit applies image correction based on the setup condition and the correction condition to the similar natural images.