A CPU selects an operation mode of an image forming apparatus by using a result of discriminating whether or not each of toner cartridges, whose information is stored in a main body NVM, is a genuine one. At that time, the CPU selects an operation mode of the image forming apparatus according to the combination of results of discriminating the toner cartridges (Y, M, C, K). For example, in a case where all the toner cartridges are genuine ones, the CPU selects an operation mode S that corresponds to the genuine one. Further, in a case where at least one of the toner cartridges is other than the genuine one, the CPU selects an operation mode N that differs from the operation mode corresponding to the genuine one.