An antenna device, including an antenna element constituted by a conductor, having a tubular shape, and including a long notch section formed to extend in an axial direction in at least a part of a side surface, a capacitor formed to bridge end portions of the notch section in a short direction, substantially at a center of the notch section in a longitudinal direction, and a power feed point formed at a position which is apart from the capacitor to a side of one end portion of the notch section in the longitudinal direction and corresponds to a side of one end portion of the notch section in the short direction.