PURPOSE: To decrease a cellar of this design in cost as it retains an excellent electromagnetic shielding property by a method wherein the ceiling of the cellar is formed of an electromagnetic wave shielding material higher than ones used for the wall and the floor of the cellar in a shielding property.

CONSTITUTION: An electromagnetic wave shielding cellar 1 consists of a ceiling 2, a wall 3, and a floor 4. The ceiling 2 is constructed with a ceiling wall material 5 and a ceiling electromagnetic shielding material 6. The wall 3 is formed of a side wall block 7 and a wall electromagnetic shielding material 8. The floor 4 is composed of a floor block material 9 and a floor electromagnetic shielding material 10. An electromagnetic shielding property of the shielding material 6 of the ceiling 2 is made higher than those of the shielding materials 8 and 10. An electromagnetic wave such as an adventitious electric wave or the like propagated from the air is partially reflected by the surface and the rest of it penetrates the earth and attenuates. An electromagnetic wave is shielded by a ceiling protective wall 12 to be attenuated and reaches to the wall 3 and the floor 4. An attenuated electromagnetic wave is shielded by the shielding materials 8 and 10. By these processes, the cost can be reduced.