An object of the present invention is to provide a method and an apparatus capable of measuring a potential of a sample surface by using a charged particle beam, or of detecting a compensation value of a variation in an apparatus condition which changes due to sample charging, by measuring a sample potential caused by irradiation with the charged particle beam. In order to achieve the object, a method and an apparatus are provided in which charged particle beams (2(a), 2(b)) emitted from a sample (23) are deflected by a charged particle deflector (33) in a state in which the sample (23) is irradiated with a charged particle beam (1), and information regarding a sample potential is detected by using a signal obtained at that time.