Sheet processing device and image forming apparatus

An image forming apparatus comprising a sheet processing device that includes

• a tray to stack a conveyed sheet;
• a pressing unit to press a vicinity of a trailing edge of a stack of sheets stacked in the tray;
• an aligning unit to align the stack of sheets stacked in the tray;
• a stapling unit to bind the stack of sheets aligned by the aligning unit;
• a discharging unit to discharge the stack of sheets bound by the stapling unit;
• and
• a control unit to control the pressing unit to keep a constant distance from a surface of a top sheet of the stack of sheets when the discharging unit discharges the stack of sheets, wherein a start position and a start timing of the pressing unit when moving to a position to keep the constant distance vary depending on binding patterns.