An antenna device forms a discone antenna and comprises a pole-shaped base member 10a composed of dielectric material. The pole-shaped base member 10a has a cone-shaped inner space formed therein. In an inside surface of the pole-shaped base member 10a, a first antenna element 11 is formed by patterning a metal conductor layer. Further, on a plain surface facing the outside of the pole-shaped base member 10a, a second antenna element 12 is formed also by circularly patterning a metal conductor layer at the side of a top of the first antenna element 11 with a predetermined space being kept between the top of the first antenna element 11 and the second antenna element 12. The first antenna element 11 and the second antenna element 12 are located with respective rotation central axes thereof being corresponding with each other.