An antenna unit includes a conductive ground plate, a first antenna element, and a second antenna element. The first antenna element includes a first end connected to a feedpoint and a second end containing an open end. A part of the first antenna element is disposed along the conductive ground plate. The second antenna element branches off the first antenna element at a branch point on the first antenna element. The second antenna element is disposed between the part of the first antenna element disposed along the conductive ground plate and the conductive ground plate. The first antenna element resonates at a first frequency. The second antenna element and a segment between the first end and the branch point of the first antenna element resonate at a second frequency that is higher than the first frequency.