An antenna device includes a coil antenna including a coil conductor wound around a winding axis, and a planar conductor. The coil antenna includes a first region in which the coil conductor overlaps the planar conductor in a plan view of the planar conductor (when viewed from the Z-direction) and a second region in which the coil conductor does not overlap the planar conductor in the plan view of the planar conductor. The line width of the coil conductor in the first region is wider than the line width of a portion (portion extending in the X-direction) of the coil conductor in the second region. Accordingly, an inductance per unit length in the circumferential direction of the coil conductor in the first region is lower than the inductance per unit length in the circumferential direction of the coil conductor in the second region.