An image forming apparatus selects a screen from a plurality of screens corresponding respectively to a plurality of gradation values and each including a pattern in which a first region to which toner is to adhere and a second region to which toner is not to adhere are defined, and forms a toner image on media. The apparatus includes a storage device for storing a minimum formable distance between first regions or second regions adjacent to each other, and a controller calculating a distance between the first regions or second regions adjacent to each other in the screen and, when the distance of the region of a screen that corresponds to a gradation value of an input image and has a first pattern is smaller than the minimum formable distance, selecting a screen corresponding to the gradation value of the input image and having a second pattern.