According to one embodiment, an antenna device comprises an antenna panel including a first transmission antenna, a first reception antenna, and a second reception antenna, and a rotation device configured to rotate the antenna panel. A first radio wave is irradiated from the first transmission antenna when a rotation angle of the antenna panel is a first angle and a reflected radio wave of the first radio wave is received by the first reception antenna and the second reception antenna. A second radio wave is irradiated from the first transmission antenna when the rotation angle is a second angle and a reflected radio wave of the second radio wave is received by the first reception antenna and the second reception antenna.