A coil section includes a primary coil which is magnetically excitable by an AC signal, and secondary coils which are provided so as to generate an inductive output in response to excitation of the primary coil. A self-oscillation circuit, including an inductance element and a capacitor, has incorporated therein the primary coil as the inductance element for self-oscillation. A target section is provided in such a manner that its relative position to the coil section varies according to a position of a target of detection, and the target section includes a magnetically responsive member disposed so that inductance of the secondary coils is varied according to the relative position. Amplitude levels of the output signals of the secondary coils are extracted, and position data of the position of the target of detection is obtained on the basis of these amplitude levels.