An ion implanter including a beam generation device that generates an ion beam, based on an implantation recipe, a plurality of measurement devices that measure beam currents of the ion beam, and a control device. The control device acquires a data set including the beam currents and an implantation parameter in the implantation recipe, and evaluates measurement validity of the beam currents of the ion beam by using the model. The implantation parameter may be one of ion species, beam energy, a beam current, a beam size, a wafer tilt angle, a wafer twist angle and an average dose. The model may be built based on a plurality of past data sets acquired during a plurality of implantation process based on the implantation recipe.