To provide an ion implanter and, an ion implanting method whereby a wafer having insufficient uniformity after ions are already implanted therein can be corrected.

An octapole scanner 6 which scans an ion beam at very small angles and a non-contact beam ammeter 8 are arranged at a beam line part 10B continuing after an ion beam interrupter 3 and an accelerating tube 4, at the rear stage of the mass separator 2 of a high voltage terminal 10A, and a beam limiting slit 9 and a wafer position detector 19 are provided at an end station part 10E. The area of a wafer W where the amount of implanting is insufficient is moved immediately below the beam limiting slit 9 by mechanical drive mechanisms 16, 17 by which a platen 13 holding the wafer position detector 19 and the wafer W is driven in X and Y directions, and scans are performed in the X and Y directions to implant ions for correction.