Abstract: An antenna device including: an antenna element; an enclosure having a wall body on which the antenna element is placed in a state of being joined to an inner surface of the wall body; and a printed substrate on which the antenna element is mounted with a leg portion of the antenna element connected to one surface of the printed substrate, which is stored inside the enclosure. Holding pieces to sandwich the antenna element between the wall body of the enclosure and the holding pieces are formed at a predetermined interval on the inner surface of the wall body of the enclosure. Respective sizes of and intervals between the holding pieces are set such that a difference between a deflection amount of the wall body and a deflection amount of the antenna element when the enclosure vibrates is less than or equal to a predetermined value.