A portable intake air sterilizing apparatus is disclosed, which allows prevention of a worker's infection with virus/bacteria and which can allow, at the same time, the worker to work comfortably. The apparatus includes a cover member C for covering one or both of the nose and the mouth, an air intake portion K for the inner space of the cover member C, and a chlorine dioxide slow-release portion J capable of releasing chlorine dioxide gas into an intake air in association with introduction of this intake air from the air intake portion K.