An image processing unit includes a region separation device and a spatial filtering device. The region separation device detects line widths of a manuscript image in which the line widths are different between a vertical line and a horizontal line and determines which of the vertical line or the horizontal line is thinner. The spatial filtering device executes an emphasizing process to make a widening ratio of a thinner line of the vertical line or the horizontal line higher than a widening ratio of the other line.