An image forming apparatus includes a housing and a first process cartridge. The first process cartridge is attachable to and detachable from the housing. The first process cartridge includes a first photosensitive drum, a first developing roller, and a developing frame. The developing frame has a toner inlet opening. The toner cartridge has a toner supply opening. The toner cartridge is positioned above the developing frame such that the toner supply opening and the toner inlet opening face with each other in upward/downward direction. In the state where the first process cartridge to which the toner cartridge is attached is attached to the housing, the toner cartridge is incapable of being detached from the first process cartridge. In a state where the first process cartridge to which the toner cartridge is attached is detached from the housing, the toner cartridge is detachable from the first process cartridge.