A tilting mechanism tilts the wafer holding portions for wafers in any direction with respect to the direction of ion beams emitted from an ion source. The tilting mechanism is comprised of a linking mechanism for transmitting the rotation of the receiving plates to the wafer holding portions, tilted links for tilting the wafer holding portions, and a shaft being coupled to the tilted links and moving in the rotary disc. The wafer holding portions provide spherical portions, and the spherical portions are inserted in the receiving plates. A pin of the preceiving plates is fitted into the groove of the wafer holding portion. The distances between the ion source and the respective wafers are maintained equal. The ion beam irradiates uniformly the respective wafers and treats uniformly the respective wafers.