An antenna device includes a casing including a metal casing portion and a feed coil. The metal casing portion includes a main surface, a side surface connected to the main surfaces, and a notch portion located in the side surface. The feed coil is disposed inside the casing to be coupled with the metal casing portion by a magnetic field, and includes a winding central portion forming a coil opening portion. The feed coil is disposed near the notch portion, with the coil opening portion directed to a region including the notch portion.