Sheet stacking apparatus and image forming system

A sheet stacking apparatus comprising:

• a stacking section adapted to stack sheets discharged in a predetermined discharge direction from a discharge section;
• a shift section adapted to shift a sheet discharged to the stacking section, in a width direction of the sheet crossing the discharge direction;
• a pair of aligning sections capable of shifting in the width direction to align end edges in the width direction of the sheet discharged to the stacking section, on a downstream side from the shift section in the discharge direction;
• a sheet pressing section provided between the pair of aligning sections to press the sheet to discharge, and
• a control section adapted to control the aligning sections and the shift section so as to adjust a relative position of the aligning sections and the end edges in the width direction of the sheet discharged,
• wherein a movable range, in a center portion, of the pair of aligning sections in the width direction is regulated by the sheet pressing section, and
• in discharging a sheet with a width narrower than the sheet capable of being aligned by the pair of aligning sections and narrower than the movable range in the center portion, to the stacking section, the control section controls the aligning sections and the shift section so that a distance between one of the pair of aligning sections and one of the end edges in the width direction of the sheet is narrower than a distance between the other one of the pair of aligning sections and the other one of the end edges in the width direction of the sheet, and that the one of the pair of the aligning sections regulates a shift of the sheet discharged to the stacking section to one direction in the width direction.