An ion implantation apparatus includes: a multistage linear acceleration unit including a plurality of stages of high-frequency resonators and a plurality of stages of focusing lenses; a first beam measuring unit disposed in the middle of the multistage linear acceleration unit and configured to allow passage of a beam portion adjacent to a center of a beam trajectory and measure a current intensity of another beam portion blocked by an electrode body outside a vicinity of the center of the beam trajectory; a second beam measuring unit disposed downstream of the multistage linear acceleration unit and configured to measure a current intensity of an ion beam exiting from the multistage linear acceleration unit; and a control device configured to adjust a control parameter of the plurality of stages of focusing lenses based on measurement results of the first and second beam measuring units.