An electric potential measuring apparatus including a substrate disposed facing a measurement object, a detecting electrode provided insulated from the substrate, and a capacity modulating unit for modulating a coupling capacity between the detecting electrode and the measurement object. In the electric potential measuring apparatus, a region with a dielectric constant less than a dielectric constant of the substrate is formed in the substrate to achieve an increase in resistivity of a portion of the substrate between detecting electrodes, or a decrease in a stray capacity between the detecting electrode and the substrate.