An object of the present invention is to provide a method and apparatus for measuring a potential on a surface of a sample using a charged particle beam while restraining a change in the potential on the sample induced by the charged particle beam application, or detecting a compensation value for a change in a condition for the apparatus caused by the sample being electrically charged. In order to achieve the above object, the present invention provides a method and apparatus for applying a voltage to a sample so that a charged particle beam does not reach the sample (hereinafter, this may be referred to as “mirror state”) in a state in which the charged particle beam is applied toward the sample, and detecting information relating to a potential on the sample using signals obtained by that voltage application.