A receiving antenna includes: an antenna element configured to receive a first radio signal for detecting a position of a capsule endoscope introduced into a subject and a second radio signal for transmitting an image captured by the capsule endoscope； a first ground connected to the antenna element； a plate on which the antenna element and the first ground are arranged； a first differential processing circuit configured to generate a differential signal based on the first and the second radio signals； a cable including one end connected to the first differential processing circuit to transmit the differential signal； a second ground provided along the cable； and a switch configured to open a path between the first ground and the second ground at a time of receiving the first radio signal, and short-circuit the path at a time of receiving the second radio signal.
