A system includes a device that is swallowed, passes through a subject, and includes a magnetic field generator generating a constant magnetic field; and a position transducer. The position transducer includes a magnetic detector detecting a magnetic filed, a magnetic field extractor extracting the constant magnetic field output from the magnetic field generator by removing a noise magnetic field component from the magnetic field detected by the magnetic detector, and a position processor calculating a position of the device in the subject based on an intensity of the constant magnetic field extracted by the magnetic field extractor.