An antenna device includes a plurality of loop elements. The loop elements are made of conductive material, and constitute a planar antenna element having N-fold rotationally symmetric shape with respect to a center portion of the planar antenna element, the N being an integer of three or more. Each of the loop elements includes at least two first elements extending in a first direction parallel to a radial direction of the planar antenna element and at least one second element extending in a circumferential direction of the planar antenna element. A ground plate is made of conductive material and opposes the planar antenna element. A power feeding line extends from the ground plate to the planar antenna element, and is electrically connected to the planar antenna element at the center portion.