Viruses, which can sometimes be a threat to humanity, can only replicate within living cells. Viruses do not replicate in cell-free environments such as in the air or tap water, but they remain infectivity under some conditions. Therefore, the virus can be transmitted to humans through droplets from the mouth or contaminated doorknobs. The epidemic of the new coronavirus led us to start research on inactivating the viruses. We have confirmed the usefulness of deep ultraviolet light for inactivating SARS-CoV-2, and have determined the wavelength, light intensity, and other conditions of deep ultraviolet light that are effective for inactivation. Virus inactivation by deep ultraviolet light has the advantage of being non-contact and non-contaminating, and can be applied to various fields including medicine. In the future, we will investigate the mechanism of virus inactivation by deep ultraviolet light and the difference in inactivation effect depending on the virus species.