A position detecting apparatus 3 includes receiving antennas 7a to 7d to receive a radio signal, transmitting antennas 8a to 8d to transmit a radio signal for power supply to a capsule endoscope 2, a first linear magnetic field generator 9 that generates a first linear magnetic field, a second linear magnetic field generator 10 that generates a second linear magnetic field, a diffuse magnetic field generator 11 that generates a diffuse magnetic field, a processing device 12 that performs a predetermined process on the radio signal received through the receiving antennas 7a to 7d, and a magnetic field sensor 13 that functions as a body-size information detector. The magnetic field sensor 13 has a function of detecting magnetic field strength at an arranged position as body-size information, and the processing device 12 has a function of controlling the first linear magnetic field generator 9 and the like based on the magnetic field strength detected by the magnetic field sensor 13. Thus, the position detecting apparatus is realized that is capable of generating a magnetic field for position detection having an optimal strength according to a difference in body sizes of subjects.