To increase a transport efficiency of an ion beam by correcting Y-direction diffusion caused by the space charge effect of the ion beam between an ion beam deflector, which separates the ion beam and neutrons from each other, and a target. An ion implantation apparatus has a beam paralleling device that bends an ion beam scanned in an X direction by magnetic field to be parallel and draws a ribbon-shaped ion beam. The beam paralleling device serves also as an ion beam deflector that deflects the ion beam by magnetic field to separates neutrons from the ion beam. In the vicinity of an outlet of the beam paralleling device, there is provided an electric field lens having a plurality of electrodes opposed to each other in a Y direction with a space for passing the ion beam and narrowing the ion beam in the Y direction.