figures the toner cartridge 40 also includes a rib 41 while the image forming process kit includes a rib 42 referring to fig4 a the image forming apparatus 30 has a pivoting cover 32 including a pair of guide rails 32a and 32b the ribs 41 and 42 can cooperate with the guide rails 32a and 32b for installation or removal of the image forming process kit on the cover 32 therefore since one of the support ribs is on the toner cartridge while the other is on the image forming process kit it is only when the two are first united via the guide rails 39a and 39b that the entire assembly can be installed on the cover 32 neither the image forming process kit 34 nor the toner cartridge 40 can be installed separately from the other therefore there cannot exist an open entrance for supplying toner to the developing unit 35 and the spillage and spread of the toner within the apparatus can be minimized fig5 a and 5 b show a further embodiment incorporated into a one component developing unit in the embodiment of fig5 a the developing unit 50 is installed in the image forming apparatus body not shown this type of image forming apparatus body is of the 34 clamshell 34 type in which an upper structure is pivotally.