A dielectric constant measuring apparatus for measuring a dielectric constant of a dielectric substance is provided with: a cantilever having a small projection on a tip side of a cantilevered electric conductor; an electrode which is placed around the cantilever and is earthed; an inductor (L) placed so as to constitute a resonance circuit together with a capacitance (Cs) in a small area of the dielectric substance that the cantilever contacts; an oscillating device connected to the resonance circuit; a demodulating device for demodulating an oscillation frequency of the oscillating device; and a dielectric constant detecting device for detecting a dielectric constant information from a demodulation signal of the demodulating. The dielectric constant measuring apparatus can be applied to an information recording/reproducing apparatus using a dielectric record medium.