Image forming apparatus, toner supply mechanism, and method of mounting and demounting toner cartridge

An image forming apparatus to which a toner cartridge is mounted comprising:

• a toner cartridge which includes a toner discharge port configured to discharge stored toner, and a shutter configured to open and close the toner discharge port;
• a toner supply unit which includes an engagement unit configured to engage with the shutter of the toner cartridge, a toner supply port configured to communicate with the toner discharge port and to receive the toner supplied from the discharge port when the shutter is open, an opening member configured to open the shutter and an elastic member configured to cause the opening member to move following the shutter by being in contact with the shutter until at least the engagement between the engagement unit and shutter is released during dismounting the toner cartridge from the apparatus;
• and
• a developing device which develops an electrostatic latent image which is formed in an image carrier using the toner which is supplied to the toner supply unit.