An ion implantation method in which an ion beam is scanned in a beam scanning direction and a wafer is mechanically scanned in a direction perpendicular to the beam scanning direction, includes setting a wafer rotation angle with respect to the ion beam so as to be varied, wherein a set angle of the wafer rotation angle is changed in a stepwise manner so as to implant ions into the wafer at each set angle, and wherein a wafer scanning region length is set to be varied, and, at the same time, a beam scanning speed of the ion beam is changed, in ion implantation at each set angle in a plurality of ion implantation operations during one rotation of the wafer, such that the ions are implanted into the wafer and dose amount non-uniformity in a wafer surface in other semiconductor manufacturing processes is corrected.