An antenna apparatus may include a conductor layer having an aperture and a slit that adjoins the aperture; and a resonance tuning component including a first element, a second element, and a third element coupled with the first and second elements. The slit may have an opening at a periphery of the conductor layer. A first gap may be arranged between the first element and the conductor layer. At least a part of the first element may be coupled with the conductor layer. A second gap may be arranged between the second element and the conductor layer. The antenna apparatus may include a capacitor and an inductor. The capacitor may be connected with the inductor in parallel between the first element and the conductor layer. The terminal device may include the antenna apparatus.