An antenna device has: a dielectric substrate; an electric supply line that has a microstrip line and is formed on the dielectric substrate; an antenna element that has a microstrip line and is formed on the dielectric substrate; and a reflector plate disposed on the dielectric substrate at a predetermined angle of inclination. The electric supply line and the antenna element deviate from a dimensional factor that allows the electric supply line and the antenna element to have an omnidirectivity, and the electric supply line and the antenna element has a dimensional factor that allows the electric supply line and the antenna element to have an elliptical directivity.