A proximity switch comprising a detection coil, a first capacitor connected in parallel with the detection coil for forming a resonant circuit, an auxiliary coil, a second capacitor connected in parallel with the auxiliary coil for forming a resonant circuit, an oscillation circuit connected to the detection and auxiliary coils which are connected in series and in reverse winding directions, and an output circuit connected to the oscillation circuit for receiving variations in output generated from the oscillation circuit, the second capacitor having a capacitance larger than that of the first capacitor so that the second capacitor has a reduced low impedance at an oscillation frequency determined by the detection coil and the first capacitor.