Sheet stacking apparatus and image forming apparatus

An image forming apparatus comprising:

• an image forming unit configured to form an image on a sheet;
• a first discharge unit disposed configured to discharge sheets with the images formed thereon;
• a first stacking unit on which the sheet discharged by the first discharge unit is stacked;
• a second discharge unit disposed below the first discharge unit and configured to discharge a sheet;
• a second stacking unit on which the sheet discharged by the second discharge unit is stacked;
• a first elevating unit configured to elevate the first stacking unit;
• an alignment unit configured to align a position of the sheet being stacked on the second stacking unit in a width direction perpendicular to a sheet discharging direction;
• a moving unit configured to move the alignment unit to one of an alignment position where a sheet is to be aligned, a retracting position retracted above the alignment position and an intermediate retracting position between the alignment position and the retracting position;
• a determining unit configured to determine a position of the first stacking unit in a vertical direction;
• and
• a control unit configured to control the moving unit based on a determination of the determining unit.