Patent ID: 8447382

Claim:
A position detecting system comprising: a body-insertable apparatus disposed in a state where it is introduced in a subject in a detection space; and an external device disposed on the outside of the subject, wherein the body-insertable apparatus includes a resonance circuit for emitting a resonance magnetic field by being induced by a drive magnetic field received from the outside, and the external device includes: a drive coil driving circuit configured to output a drive signal having a predetermined frequency; a drive coil configured to receive the drive signal and to generate the drive magnetic field in the detection space based on the drive signal; a sense coil configured to detect the resonance magnetic field and to output a detection signal; a position deriving circuit configured to derive position information of the resonance circuit by using the detection signal; a current detecting circuit configured to detect a current amplitude value of the drive signal input to the drive coil; and a drive magnetic field generation control circuit configured to calculate an amplitude value of a drive signal which is to be output by the drive coil driving circuit based on the current amplitude value, detect a degree of stability of the drive magnetic field on the basis of whether a sharp change occurs in the calculated amplitude value, and control the position deriving circuit to derive position information on the basis of the detected degree of stability of the drive magnetic field.