The ion implanter includes a deflecting electrode and a shield member. The ion beam has a ribbon shape. The deflecting electrode deflects at least a part of the ion beam in a long side direction toward a short side direction of the ion beam, based on a result measured of a beam current density distribution in the long side direction. The shield member partially shields the ion beam deflected by the deflecting electrode. The deflecting electrode includes a plate electrode and an electrode group including plural electrodes. The electrode group is disposed to face the plate electrode to interpose the ion beam between the plate electrode and the electrode group. The plate electrode is electrically grounded, and the plurality of electrodes are electrically independent from each other. Each of the plurality of electrodes is connected to an independent power source from other power sources to perform a potential setting.