An antenna device includes a conductor surface in which an opening having an open edge portion in communication with the outside is provided, a feed element including a first coil connected to the feed element and a second coil magnetically coupled to the first coil, a first mounting portion disposed in the open edge portion and connected to a first end of the second coil, and a second mounting portion disposed in the open edge portion in a state isolated from the first mounting portion and connected to a second end of the second coil. The first mounting portion and the conductor surface are directly or indirectly conducted to each other, and the second mounting portion and the conductor surface are directly or indirectly conducted to each other. A loop is defined around the opening through the first mounting portion, the second mounting portion, and the second coil.