A processing device 12 includes, as a mechanism for controlling the strength of a position detecting magnetic field, a recording unit 43 that records past position detection results, a moving speed calculator 48 that calculates moving speed of a capsule endoscope 2 based on a change of the position of the capsule endoscope 2, a range calculator 49 that calculates a range in which the capsule endoscope 2 is positioned based on the calculated moving speed and the past positions of the capsule endoscope 2, and a magnetic-field strength controller 50 that controls the strength of the magnetic field generated by the second linear magnetic-field generating unit 10 and the diffuse magnetic-field generating unit 11 based on the calculated range. The processing device 12 achieves a position detecting apparatus capable of forming the necessary and sufficient position detecting magnetic field, at the time of performing position detection of a detected object such as the capsule endoscope, by using the position detecting magnetic field having position dependency.