A change of a beam current of an ion beam which passes an outside of the side of a forestage beam restricting shutter, and which is incident on a forestage multipoints Faraday is measured while the forestage beam restricting shutter is driven in a y direction by a forestage shutter driving apparatus in order to obtain a beam current density distribution in the y direction of the ion beam at a position of the forestage beam restricting shutter. A change of a beam current of the ion beam which passes an outside of the side of a poststage beam restricting shutter, and which is incident on a poststage multipoints Faraday is measured while the poststage beam restricting shutter is driven in the y direction by a poststage shutter driving apparatus in order to obtain a beam current density distribution in the y direction of the ion beam at a position of the poststage beam restricting shutter. By using these results, an angle deviation, a diverging angle, and/or a beam size in the y direction of the ion beam can be obtained.