An image forming apparatus includes an image forming unit having an exposure unit and a developing unit; a detection unit configured to detect a thickness and an area ratio of a toner layer of a pattern image formed by the image forming unit; a storage unit configured to store data indicating permissible ranges for the thickness and the area ratio of the toner layer; and a correction unit configured to change, when the thickness or the area ratio of the toner layer detected by the detection unit falls outside the corresponding permissible range indicated by the data stored in the storage unit, a spot diameter of the laser beam so that the thickness and the area ratio of the toner layer respectively fall within the permissible ranges.