A radiation level reducing device, including: a metal plate for covering surface of an electromagnetic wave generation source for radiating an electromagnetic wave; a cover region, set within a plane of the metal plate, for covering the surface; and a plurality of slits formed to a band-shape in the cover region, and spaced apart from each other, wherein each of the plurality of slits includes, a drawing slit extending towards a central part of the cover region from an intense electric field position where an electric field generated in between the electromagnetic wave generation source by the electromagnetic wave is stronger than other positions at an outer periphery of the cover region, and a coupling slit extending so as to line in parallel to another slit from an end in the central part direction of the cover region in the drawing slit.