An antenna device includes a T-shaped element having a first end part, a second end part, and a third end part, the first end part being a feeding point, the T-shaped element being bifurcated at an intermediate point; and a stub having one end connected between the intermediate point and the second end point and another end connected to ground, the stub forming a π-shaped configuration with the T-shaped element; wherein a length of a first line between the first end part and the second end part is longer than a length of a second line between the first end part and the third end part; and the length of the first line and the length of the second line correspond to a first resonance frequency and a second resonance frequency.