After a sheet has once passed through a punching position, a conveyance roller pair conveys the sheet backward to the punching position. A lateral registration detection sensor detects a side edge position of the sheet in a width direction. When a sheet processing apparatus corrects the side edge position of the sheet by controlling a shift unit for moving the sheet in the width direction so as to correct the side edge position of the sheet, the sheet processing apparatus sets a shifting amount of the sheet to a value that is a predetermined amount greater than a shifting amount required to correct the side edge position of the sheet according to the side edge position of the sheet detected by the lateral registration detection sensor. After the sheet has passed through the die hole the sheet processing apparatus sets the shifting amount to the required value.