An image forming apparatus includes a pattern forming unit which forms a light amount adjustment pattern on an image carrier belt, a light amount control unit which controls the amount of light irradiating the image carrier belt and pattern, a detection sensor which detects reflected light amounts from the image carrier belt and pattern with respect to the irradiating light amount and stores the detection results in a storage unit, a calculation unit which calculates the correspondence between the irradiating light amount and the reflected light amounts from the image carrier belt and pattern on the basis of the detection results and stores the calculation results in the storage unit, and a light amount decision unit which decides, on the basis of the calculation results, a light amount at which the difference between the reflected light amounts from the image carrier belt and pattern exhibits a value set in advance.