Provided are a method and an apparatus for inactivating bacteria or viruses attached to an object while suppressing generation of a strange odor. The method for inactivating bacteria or viruses includes a step (a) of irradiating with ultraviolet light having an optical output at a specific wavelength in a range of 200 nm to 235 nm. The step (a) is a step of irradiating with the ultraviolet light is performed so that an irradiance (X) [mW/cm2] (X>0) and an integrated irradiation dose within two hours (Y) [mJ/cm2] satisfy the following formula (1)

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