An apparatus for measuring a surface potential of an object on an underlying structure is disclosed. A relatively-moving mechanism moves a probe and a second support member relative to each other until the probe faces a reference structure on the second support member, an electric potential measuring device measures the surface potential of the reference structure through the probe, the controller calibrates the electric potential measuring device such that a measured value of the surface potential of the reference structure becomes 0, the relatively-moving mechanism moves the probe and a first support member relative to each other until the probe faces the object on the first support member after the calibration, and the electric potential measuring device measures the surface potential of the object through the probe.
