An image forming apparatus includes a rotary unit that has a rotary shaft,
and a plurality of development devices each of which has a constituent
unit, the development devices provided around the rotary shaft; and a
plurality of state detection units that detects at least one of states of
the development devices and states of the constituent unit; wherein the
rotary unit is rotated so that the development devices sequentially pass
a development position facing a photosensitive member; wherein when any
of the development devices is located at the development position, the
development device makes an electrostatic latent image on the
photosensitive member visible; and wherein each of the state detection
units detects at least one of the development devices and the states of
the constituent unit during a single stop of rotation of the rotary unit.