An image forming apparatus includes: a frame; a photosensitive drum that is supported by the frame; a developing unit that is rotatable around a rotating shaft supported by the frame and includes a developing frame having a toner receiving port and a developing roller; a toner cartridge that has a toner supply port; and a seal member that positioned a circumference of the toner receiving port and is deformable, wherein the seal member has a communication opening, which communicates between the toner receiving port and the toner supply port in a state where the toner cartridge is mounted to the frame, and the seal member has a first end and a second end, wherein when the developing unit rotates to approach the toner cartridge, the first end of the seal member and the second end of the seal member are configured to be compressed.