A system includes a device that is swallowed, passed through a subject, and includes a magnetic field generator generating a constant magnetic field; and a position transducer. The position transducer includes a plurality of magnetic detectors detecting intensities of a magnetic filed, first and second fixing units that fix at least one magnetic detector to the subject, respectively, a position fluctuation detector that detects a fluctuation of positional relation between the first fixing unit and the second fixing unit, a coordinate calibrating unit that calibrates position coordinate of the magnetic detector based on a detection result by the position fluctuation detector. The system also includes a position processor that calculates a position of the device in the subject based on an intensity of the constant magnetic field detected by the magnetic detector and the position coordinate of the magnetic detector after calibration by the coordinate calibrating unit.