A development rotary unit is made loadable with a development cartridge having no conditioning fin and containing a black toner in addition to a development cartridge containing a black toner and having a conditioning fin for agitating and re-supplying the toner contained therein. In the case of formation of an image which necessitates an operation of re-supplying a toner by rotating the development rotary unit in order to form it with the development cartridge, the formation of the image is started by moving the development cartridge to the developing position.