a large - capacity paper feeding apparatus comprising a main unit which is to be mounted on one side of an image forming apparatus , is movable on a floor and is configured to feed paper sheets to the image forming apparatus , a caster which is provided at a bottom of the main unit and is to contact the floor to allow the main unit to move smoothly on the floor , and a mounting device which is moved to a first position to make the caster contact the floor and to a second position to retract the caster upward from the first position .