An image forming apparatus includes a pattern formation unit which forms a first gradation screen pattern on an image carrier unit at a non-image formation operation, a gradation characteristic determination unit which determines a gradation characteristic from the first gradation pattern formed by the pattern formation unit, a first gradation correction characteristic determination unit which determines a first gradation correction characteristic from the gradation characteristic determined by the gradation characteristic determination unit, a characteristic detection unit which detects a change characteristic in the image forming apparatus just before image formation, a pattern correlation characteristic correction unit which determines a pattern correlation characteristic corresponding to the change characteristic detected by the characteristic detection unit and a second gradation correction characteristic determination unit which determines a second gradation correction characteristic by performing an arithmetic operation on the first gradation correction characteristic and the pattern correlation characteristic.