When a second detector determines that a character image has a halftone (YES in #1) and a third detector (48) determines that a font size of the character image is equal to or greater than a threshold value β and equal to or smaller than a threshold value α (YES in step #4), a fourth detector determines whether a presently focused pixel constitutes a particular portion of a character (step #5). When the fourth detector determines that the pixel data of the presently focused pixel constitutes the particular portion of the character (YES in step #5), the image processing section sets the pixel data to be subjected to a second screen processing which is performed at a higher gradation level (step #6).