PURPOSE: To provide a protective structure resistant to electromagnetic interference in low-frequency range at low cost.

CONSTITUTION: A disk-type antenna 4 is provided on a face 1a vertical to the direction (P) in which electromagnetic waves are reduced. A terminating resistor 5 matching with the characteristic impedance of the antenna 4 is provided between the antenna terminals. Even a small disk-type antenna 4 has a gain in a wide frequency range. The energy captured by the antenna 4 is consumed by the terminating resistor 5, and the shielding effect becomes larger than a conventional one. In addition directivity in all directions can be obtained, and the shielding effect is sufficient even for the electromagnetic wave in any direction other than the vertical direction to the disk-type antenna.