A position detecting system including: a detected object disposed in a space; and an external device disposed outside the space, wherein the detected object includes a resonant circuit, and the external device includes at least two drive coils; at least two drive-signal input units; at least one sense coil; a signal adjustment unit that adjusts a phase or amplitude of a drive signal using an evaluation function for evaluating the phase or the amplitude, based on an intensity of the magnetic field; and a position deriving unit that derives a position of the detected object based on a magnetic field detected by the sense coil, wherein the evaluation function derives a solution by adding or multiplying a weight set according to a positional relation between each drive coil and each sense coil to or by an intensity of a magnetic field detected by the sense coils.