Image forming apparatus and optional sheet feeding device

An image forming apparatus comprising:

• an image forming apparatus main body including an image forming unit that forms an image on a sheet, a detachable main body sheet feeding tray that holds the sheet, a sheet feeding unit that feeds the sheet from the main body sheet feeding tray toward the image forming unit, and a controller that controls at least the sheet feeding unit;
• wherein the image forming apparatus main body is capable of being added an optional sheet feeding device that feeds the sheet toward the image forming unit on a lower side of the main body sheet feeding tray;
• a portion of the main body sheet feeding tray constitutes a portion of a transport path of the sheet which extends from the optional sheet feeding device to the image forming unit when the main body sheet feeding tray is attached to a proper position;
• and
• when the optional sheet feeding device comprises a detector that detects whether or not the main body sheet feeding tray is attached to the proper position, the controller controls operations of the image forming apparatus main body and the optional sheet feeding device based on a detection result of the detector.