An antenna device includes a substrate, and a dual-band antenna disposed on a surface of the substrate. The dual-band antenna includes a feed-in section, a first radiator arm, a second radiator arm, a third radiator arm, and a ground section. The feed-in section is for signal feed-in, and has opposite first and second ends. The first radiator arm extends from the first end of the feed-in section and is parallel to the feed-in section. The second radiator arm is connected to the second end of the feed-in section and extends parallel to the feed-in section. The third radiator arm is disposed adjacent to and extends parallel to the first radiator arm in a manner that the feed-in section is disposed between the third radiator arm and the second radiator arm. The ground section is connected to the third radiator arm.