A method and an apparatus capable of selectively damaging and killing tumor cells includes a step of irradiating tumor cells with a UV pulse flash having continuous emission spectra ranging at least from 230 to 270 nm, outside a living body of a human or a living body of a non-human animal or in a living body of a non-human animal. The UV pulse flash may have an accumulated irradiation amount per unit area that is achieved at a distance of 8 cm from a light source having an integrated output of, for example, 90, 180-7100 or 14200 J.
