An antenna device includes a first structural layer and a second structural layer. The first structural layer is located at a first plane and includes first antenna structures, a main feeding point, a first subsidiary feeding point and a transmission line. The main feeding point is located between a first transmission line segment and a second transmission line segment, which are respectively connected to different first antenna structures. First transmission paths are formed from the main feeding point to a part of the first antenna structures, and the first transmission paths pass through the first subsidiary feeding point. Second transmission paths are formed from the main feeding point to another part of the first antenna structures. The second structural layer is located at a second plane and includes a conductor, and at least part of projections of the first antenna structures projected onto the second plane surrounds the conductor.