An image forming apparatus, having: a rotary developing unit, to and from which a plurality of developing cartridges storing developers are attached and detached and which moves one of the attached developing cartridges to a developing position by being rotated around a rotation axis; a drive motor that rotates the rotary developing unit; and a controller that controls a torque of the drive motor in response to a condition of the developing cartridges to be attached to the rotary developing unit or a condition of the rotary developing unit.