An ion implanter includes: a main body which includes a plurality of units which are disposed along a beamline along which an ion beam is transported, and a substrate transferring/processing unit which is disposed farthest downstream of the beamline, and has a neutron ray source in which a neutron ray is generated due to collision of a ultrahigh energy ion beam; an enclosure which at least partially encloses the main body; and a neutron ray scattering member which is disposed at a position where a neutron ray which is emitted from the neutron ray source is incident in a direction in which a distance from the neutron ray source to the enclosure is equal to or less than a predetermined value.