An antenna device includes a plate-shaped radiating element, a frame-shaped radiating element arranged to surround the plate-shaped radiating element, and a feeding unit that includes a feeding circuit and a frequency stabilizing circuit and that is connected between the plate-shaped radiating element and the frame-shaped radiating element. The plate-shaped radiating element and the frame-shaped radiating element are connected to the feeding circuit through the frequency stabilizing circuit as a result of a first terminal portion of the frequency stabilizing circuit being connected to the frame-shaped radiating element, a second terminal portion of the frequency stabilizing circuit being connected to the plate-shaped radiating element, and a third terminal portion of the frequency stabilizing circuit being connected to the feeding circuit.