An antenna apparatus that can precisely receive a radio signal transmitted from a capsule endoscope introduced in an inside of a subject is provided. The antenna apparatus includes: a first receiving antenna 41 and a second receiving antenna 42 respectively disposed at positions which are in an equal distance from a reference point O 1 and face each other with the reference point O 1 therebetween a third receiving antenna 43 and a fourth receiving antenna 44 disposed at positions on a plane, a gravity center of the third receiving antenna 43 and a gravity center of the fourth receiving antenna 44 being in an equal distance from the reference point O 1 on the plane, a straight line connecting the gravity centers of the third receiving antenna 43 and the fourth receiving antenna 44 being at an angle of 90 degrees with respect to a straight line connecting gravity centers of the first receiving antenna 41 and the second receiving antenna 42 and a fifth receiving antenna 45, a sixth receiving antenna 46, a seventh receiving antenna 47, and an eighth receiving antenna 48 disposed respectively at positions on the plane, gravity centers of the fifth receiving antenna 45 to the eighth receiving antenna 48 being on straight lines different from each other, which are rotated by an angle of 45 degrees from the straight line connecting the gravity centers of the first receiving antenna 41 and the second receiving antenna 42 and the straight line connecting the gravity centers of the third receiving antenna 43 and the fourth receiving antenna 44, respectively.
