An image forming apparatus which can expand the space of a discharging unit includes a scanner rotating unit provided below a scanner unit to rotate the scanner unit, to open the top of a discharging unit, and to expand a space of the discharging unit if the collective height of sheets accumulated in the discharging unit reaches or exceeds a predetermined value, and a control unit arranged to detect whether the collective height of the sheets accumulated in the discharging unit reaches or exceeds the predetermined value to operate the scanner rotating unit in accordance with the detection result.