An antenna device includes: a ground electrode; a first dielectric layer which is provided on one surface of the ground electrode; a feed plate which is provided on a surface of the first dielectric layer opposite from the ground electrode, and which is shorted to the ground electrode; a feed line which feeds to the feed plate; a second dielectric layer which is provided in such a manner as to sandwich the feed plate in combination with the first dielectric layer; and a radiation electrode which is provided on a surface of the second dielectric layer opposite from the feed plate, and which is fed by being electrically connected to the feed plate at a feed point and thereby radiates or receives a radiowave with a first frequency.