In an ion implantation method, ion implantation into a substrate is performed while changing a relative positional relation between an ion beam and the substrate. A first ion implantation process in which a uniform dose amount distribution is formed within the substrate and a second ion implantation process in which a non-uniform dose amount distribution is formed within the substrate are performed in a predetermined order. Moreover, a cross-sectional size of an ion beam irradiated on the substrate during the second ion implantation process is set smaller than a cross-sectional size of an ion beam irradiated on the substrate during the first ion implantation process.