A position detecting apparatus includes receiving antennas to receive a radio signal, transmitting antennas to transmit a radio signal for power supply to a capsule endoscope, a first and second linear magnetic field generators that generate first and second linear magnetic fields, a diffuse magnetic field generator that generates a diffuse magnetic field, a processing device that performs a predetermined process on the radio signal, and a magnetic field sensor that functions as a body-size information detector. The magnetic field sensor detects magnetic field strength at an arranged position as body-size information, and the processing device controls the first linear magnetic field generator based on the magnetic field strength detected by the magnetic field sensor. Thus, the position detecting apparatus is capable of generating a magnetic field for position detection having an optimal strength according to a difference in body sizes of subjects.