A system for detecting a position in a subject includes a test capsule (2) having therein a permanent magnet, and a position transducer (3) that detects the position of the test capsule (2) based on the intensity of a constant magnetic field generated from the permanent magnet provided in the test capsule (2). The position transducer (3) has magnetic field detectors (6a to 6h), an inclination sensor (7), a horizontal in-plane azimuth sensor (8), fixing members (9a, 9b) for fixing the magnetic field detectors (6a to 6h) and the like to a subject (1), and a position information processor (10) that derives the distance between the test capsule (2) and each of the magnetic field detectors (6a to 6h) based on the magnetic field intensities detected by the magnetic field detectors (6a to 6h) and derives the position of the test capsule (2) based on the derived distances.
