To provide an electric potential sensor having an inexpensive structure, capable of suppressing increase in the electrostatic capacity between a detection electrode and a tuning fork oscillator to a minimum, and capable of making cost reduction of the detection electrode and maintenance of its performance coexist.

The electric potential sensor is composed of the detection electrode counterposed to a surface to be measured being an object of potential measurement, and the tuning fork oscillator composed of two oscillating arms for periodically changing the facing area between the detection electrode and the surface to be measured. In this case, the detection electrode is made of metal and has a cylindrical structure, and its cost can be reduced while maintaining the conventional performance.