The character edge area determining unit (21) determines a character edge area in input image data.The output image processing unit (12) performs an image process for a target pixel in the determined character edge area in order to adjust a toner consumption amount in accordance with the number of continuous edge pixels (i.e. continuous pixels that belong to the character edge area) included in a reference window of which a center is set on the target pixel and an average value of pixel values of the continuous edge pixels.