An antenna device includes a ground; a monopole antenna including a first section running from a feeding point along the ground, a second section running in a direction away from the ground, and a third section running along the ground, the monopole antenna having a length corresponding to ¼ of a wavelength at a first resonance frequency; a parasitic element including a first section whose end is connected to the ground in the vicinity of the end of the first section of the monopole antenna and that runs in a direction away from the ground, and a second section, the parasitic element having a length corresponding to ¼ of a wavelength at a second resonance frequency; and a dipole antenna provided along the third section of the monopole antenna and the parasitic element, the dipole antenna having a length corresponding to ½ of a wavelength at a third resonance frequency.