An image forming apparatus which includes a main body, an image forming unit to form an image on a printing medium, a plate to open and close a first side of the main body; a pickup unit which includes a driven gear to rotate in forward and backward directions, a pickup roller to receive a driving force from the driven gear to pick up the printing medium disposed on the plate, and a support frame to rotatably support the pickup roller and to interlock with the forward and backward rotations of the driven gear to move toward and away from the plate, a driving source to drive the image forming unit and the driven gear, and a blocking gear disposed between the driven gear and the driving source, to prevent the support frame, spaced apart from the plate, from moving toward the plate.