PURPOSE: To get enough electromagnetic wave screen property as to leaked electromagnetic waves by arranging small-diameter holes at regular pitches and angles all over the surface of a cover.

CONSTITUTION: Circular holes 1mm in diameter are arranged at 2mm in pitch and 60° in angle all over the surface of a cover 1. Thereupon, in case that the electromagnetic waves leaked from the inside of electronic equipment is radiated to the cover 1, an induced current arises in the cover 1, and the section of the circular hole 2 becomes electrically vacant. Here, taking the frequency of the electromagnetic waves leaking usually from the inside of the electronic equipment into consideration, it is several Hz to several hundred MHz, and its wavelength λ is in the range from several m to about 0.3m. Taking enough electromagnetic wave screen property into consideration, the dimension of an electrically vacant section, in short, the dimension of opening should be set to one-hundredth to two-hundredth the wavelength λ. It becomes about 1.5mm. Accordingly, since the circular holes 2, 1mm in diameter is adopted, it can fulfill enough screen property up to a maximum of 1GHz.