To make density deterioration due to a halo phenomenon more inconspicuous.

A rendering part 301 converts a drawing instruction from an application into image data for one page to be expressed by pixel values from zero to 255. An image input part 302 stores the image data from the rendering part 301 to output the pixel value of a pixel position to be requested from an image correction part 303. The image correction part 303 sequentially considers each pixel of an input image as a noticing pixel, and when the noticing pixel is the one whose density is deteriorated by the halo phenomenon, raises the pixel value.