Toners of the same color but with different characteristics are stored in the toner cartridges. For example, toners for high image quality (High Grade) with small particle diameter are stored in some toner cartridges and toners for low image quality (Low Grade) are stored in other toner cartridges. In this case, case, the mode of forming images using small particle diameter toner for high image quality using an image forming engine and the mode of forming images using a toner for low image quality using another image forming engine are executed by the image forming apparatus.