A system includes a device swallowed, passing through a subject, and including a constant magnetic field generator generating a constant magnetic field; and a position transducer. The position transducer includes a magnetic detector, a calibration magnetic field generator, a magnetic detector detecting an intensity of a magnetic field, a coordinate calibrating unit, and a position processor. The calibration magnetic field generator is disposed at a fixed relative position to the subject, and generates a calibration magnetic field for position calibration of the magnetic detector. The coordinate calibrating unit calibrates a position coordinate of the magnetic detector using an intensity of the calibration magnetic field. The position processor calculates a position of the device in the subject based on the intensity of the constant magnetic field and the position coordinate of the magnetic detector calibrated.