A replacing mouth 5 for replacing each of toner cartridges 40 is provided at such a position that when any of developer units 32 stops at a developing position 38, the toner cartridge 40 adjacent to the pertinent developer unit 32 and supplementing the toner to another developer unit 32 different from the pertinent developer unit 32 can be replaced. Further, an information reading device 46 for reading the information from the storage medium 42 included in each of the toner cartridges 40 reads the information from the storage medium when any of the developer units 32 is located at the developing position 38.