To provide an antenna device that arrests damage caused by the direct attack of thunder and has two-way directivity in order to protect a transmitter/receiver, a coaxial cable, an antenna and the like which are wireless facilities.

In a half wavelength dipole antenna with which two radiators (1), (2) are linearly protruded near the top of a mast of the antenna, a Faraday cage is configured so as to surround the outer frame of the radiators (1), (2) with a long and rectangular metallic frame (4) in which rods (4a), (4b) disposed in parallel with the linear direction of the radiators (1), (2) are made long sides using a wire, a rod, a pipe or the like within a perpendicular surface including the radiators (1), (2) or a perpendicular surface proximate to the radiators (1), (2), and a ground line (5) linked to the metal frame is fixed on a ground pole (6) buried in the earth. In a half wavelength dipole antenna for horizontal polarization in which two radiators (1), (2) are horizontally and linearly provided at left and right sides, and in a half wavelength dipole antenna for vertical polarization in which two radiators (1), (2) are vertically and linearly provided, a long and rectangular metallic frame (4) is also disposed in the linear direction of the radiators (1), (2) so as to surround the outside of the radiators (1), (2) within a perpendicular surface including the radiators (1), (2) or a perpendicular surface proximate to the radiators (1), (2), length of rods (4a), (4b) which are long sides of the metallic frame (4), is defined as the length of one wavelength, and length of rods (4c), (4d) which are short sides, is defined as the length of a half wavelength.