An ion implantation apparatus includes a beam parallelizing unit and a third power supply unit. The beam parallelizing unit includes an acceleration lens, and a deceleration lens disposed adjacent to the acceleration lens in an ion beam transportation direction. The third power supply unit operates the beam parallelizing unit under one of a plurality of energy settings. The plurality of energy settings includes a first energy setting suitable for transport of a low energy ion, and a second energy setting suitable for transport of a high energy ion beam. The third power supply unit is configured to generate a potential difference in at least the acceleration lens under the second energy setting, and generate a potential difference in at least the deceleration lens under the first energy setting. A curvature of the deceleration lens is smaller than a curvature of the acceleration lens.