An image forming apparatus includes: an image forming unit configured to form an image pattern on a medium, a predetermined image repeatedly appearing in a first cycle in a sub scanning direction in the image pattern; a density detector configured to optically detect a density of the image pattern in the sub scanning direction; a cyclic image detector configured to detect a feature image having a second cycle corresponding to the first cycle in accordance with a result of the detection; and a state determining unit configured to determine whether a cycle depending on an outer circumference of a rotary member included in the image forming apparatus corresponds to the second cycle when the feature image is detected by the cyclic image detector, and determine that a state of the rotary member has deteriorated when the cycle depending on the outer circumference is determined to correspond to the second cycle.