An ion implantation apparatus reciprocally scans an ion beam extracted from an ion source and passed through a mass analysis magnet apparatus and a mass analysis slit and irradiates to a wafer. The ion beam is converged and shaped by providing a first quadrupole vertical focusing electromagnet at a section of a beam line from an outlet of the mass analysis magnet apparatus before incidence of the mass analysis slit and providing a second quadrupole vertical focusing electromagnet having an effective magnetic field effect larger than that of the first quadrupole focusing electromagnet at a section of the beam line from an outlet of the mass analysis slit before incidence on the beam scanner.