A charged particle optical system includes an aberration corrector 209 that corrects aberration of a charged particle beam and has multipoles of a plurality of stages. The aberration corrector generates a plurality of multipole fields in a superimposed manner for each of the multipoles of the plurality of stages in order to correct the aberration of the charged particle beam. In order to reduce the influence of a parasitic field due to distortion of the multipole, for a first multipole field to be generated in a multipole of any stage among the plurality of stages, a value of a predetermined correction voltage or correction current to be applied to a plurality of poles for generating the first multipole field is corrected so as to eliminate movement of an observation image obtained based on electrons detected from a detector 215 by irradiating a sample with the charged particle beam before and after the first multipole field is generated.