An image forming apparatus may include a main body having a developing apparatus, a driving source configured to generate power in the main body, a driven unit configured to receive the power from the driving source to be operated, a supply cassette configured to be detachable from the main body and in which printing media are stacked, and an opening/closing unit configured to receive power from the driving source configured to drive the driven unit to move the supply cassette back and forth. Accordingly, the supply cassette can be automatically opened and closed to provide user convenience.