Method of sheet alignment and method of post-processing comprising the same and method of image formation

A method of sheet alignment comprising the steps of:

• carrying a sheet from a sheet discharging port;
• transferring the sheet on a tray device toward a sheet end regulating device;
• moving the sheet on the tray device in a width direction orthogonal to the sheet discharging direction for widthwise alignment;
• and
• abutting again the sheet on the tray device against the sheet end regulating device while the sheet is in the widthwise alignment;
• wherein (1) when the sheet on the tray device is transferred toward the sheet end regulating device, the sheet is transferred at a predetermined speed, (2) before the sheet abuts against the sheet end regulating device, the predetermined speed is reduced to provide a conveying force to the sheet without stopping, (3) after the sheet abuts against the sheet end regulating device with said conveying force, the conveying force applied to the sheet is increased, and (4) while the conveying force is being applied continuously to the sheet, the sheet is aligned in the width direction to thereby prevent skewing of the sheet relative to the sheet end regulating device.