A sheet processing apparatus includes a sheet stacking unit where sheets to be processed are stacked, a regulating member, a sheet waiting unit, a first moving unit, a second moving unit, and a control unit. The regulating member abuts on one edge of sheets conveyed to the sheet stacking unit. The sheet waiting unit keeps sheets waiting, stacks the waiting sheets displaced sequentially, and then conveys the sheets to the sheet stacking unit. The first moving unit sequentially moves the conveyed sheets, starting from a lowermost sheet, to be abutted against the regulating member. The second moving unit moves the conveyed sheets to the first moving unit. The control unit controls a moving speed of the second moving unit so that a next sheet does not reach the first moving unit until the sheet moved by the first moving unit is abutted against the regulating member.