Developing unit and image forming apparatus including the same

An image forming apparatus comprising:

• a body;
• and
• a developing unit detachably installed at the body through an opening provided at the body, the developing unit including:
• a developing cartridge detachably installed within the body through an opening provided at the body, the developing cartridge being provided with a waste developing agent outlet to discharge waste developing agent;
• a developing agent cartridge detachably mounted to the developing cartridge, the developing agent cartridge comprising a developing agent storage section to supply developing agent to the developing cartridge, and a waste developing agent storage section provided with a waste developing agent inlet to receive the waste developing agent discharged from the waste developing agent outlet;
• a shutter member to open and close the waste developing agent inlet when the developing agent cartridge is mounted to or separated from the developing cartridge;
• and
• an elastic member to elastically support the shutter member so that the shutter member closes the waste developing agent inlet,
• wherein the developing cartridge comprises a waste developing agent discharge section provided with the waste developing agent outlet, and the waste developing agent discharge section pushes the shutter member when the developing agent cartridge is mounted to the developing cartridge, thereby causing the shutter member to move to open the waste developing agent inlet.