The position of an antenna incorporated in a capsule-type endoscope 3 that moves in a body is estimated using a plurality of antennae, and where the distance dij between two positions Pti and P(t−1)j estimated at adjacent times falls within a predetermined value, pieces of information for these positions are related to each other and stored in a memory as connection information. Subsequently, processing for searching for a route from the connection information stored in the memory and calculating a track is performed.