There is provided an antenna device including: a finite ground plane; a feeding point; feed antenna elements arranged in a radial fashion around the feeding point at a height from the finite ground plane; a selector switch to connect a first end of a feed antenna element selected from the feed antenna elements to the feeding point; and parasitic elements arranged correspondingly to the feed antenna elements, in which a first end thereof is connected to the finite ground plane and a portion including a second end thereof is capacitively coupled with the feed antenna element corresponding thereto, wherein a first length of the parasitic element is approximately a quarter of a wavelength of a radio frequency to be used, and a length from the second end of the feed antenna element to the feeding point is shorter than the first length of the parasitic element.