Patent ID: 7606505

Claim:
An image forming apparatus, comprising: a plurality of image forming units detachably provided in the image forming apparatus and including at least two common image forming units having a common structure, each including a development device; a toner supply device configured to supply toners of different colors to corresponding development devices of the plurality of image forming units; a common-unit detection device configured to detect each one of the at least two common image forming units at installation thereof; an initial operation execution device configured to execute an initial operation of supplying an amount of toner to a development device of each one of the at least two common image forming units detected by the common-unit detection device and mixing to charge the toner by friction for a preset time period before a formation of a reference image on an image carrier; and a determination device configured to detect a status as to whether the toner in the development device is charged to a threshold level upon completion of the initial operation, and to determine whether to mix the toner one more time for another time period based on the status detected.