An antenna apparatus capable of attaching a plurality of antennas to a subject in a position information' estimation system that estimates the position of a capsule endoscope, an antenna, and an antenna holder that holds the antenna are provided. An antenna apparatus (4) according to the present invention is an antenna apparatus that acquires information from a body-insertable apparatus that is inserted into a subject and moves inside the subject. The antenna apparatus includes an acquisition antenna (4) which includes a piece of polygonal sheet portion (40) to which a plurality of receiving antennas is fixed and in which an positioning hole (49) is formed at a position that is shifted from the center of the polygonal sheet portion (40)； and an antenna holder (7) that includes an container portion (71) which is configured to accommodate the acquisition antenna (4) and in which an positioning hole (73) corresponding to the positioning hole (49) of the acquisition antenna (4) is formed.
