An antenna device according to an aspect of the present invention includes a plurality of radiation elements, an array antenna, a skin material, a core material and an antenna casing. The plurality of radiation elements transmit radio waves of a predetermined frequency. The array antenna has a radiation surface and a back surface opposite to the radiation surface. The plurality of radiation elements are disposed on the radiation surface. The skin material is disposed in a direction in which the skin material faces the radiation surface. The core material is disposed between the array antenna and the skin material, and has a plurality of through-holes. The antenna casing is disposed in a direction in which the antenna casing faces the back surface. A distance between centers of adjacent through-holes of the through-hole is equal to or less than one-half of a wavelength corresponding to the predetermined frequency.