An antenna apparatus allows for internal impedance matching by employing an internal matching device therein. The antenna apparatus includes a board body formed of a dielectric material and having a flat structure. The antenna apparatus also includes an antenna device disposed on an upper surface of the board body, and the internal matching device disposed on a lower surface of the board body. The antenna device extends from a feed point and has a first impedance. The internal matching device is connected to the antenna device and has a second impedance used for matching the first impedance with a reference impedance. The antenna device and the internal matching device resonate at the reference impedance in a specific frequency band when a voltage is supplied through the feed point.