An antenna device includes: a balanced transmission line to which an unbalanced transmission line is connected at one end; and antenna elements respectively provided on both sides of the balanced transmission line, in which at least one of the antenna elements, in a case where a first point and a second point are set, the first point being separated from a position on one end side of the balanced transmission line in a direction substantially orthogonal to the balanced transmission line, the second point being separated from a position on another end side of the balanced transmission line in a direction substantially orthogonal to the balanced transmission line, has a shape including the second point and an oblique line or side connecting the other end side of the balanced transmission line with the first point, the other end side of the balanced transmission line is connected to a vertex portion of the antenna element, a linear element is provided extending from a position of the first point of the antenna element toward the one end side of the balanced transmission line, and the antenna element and the linear element include a conductor.