a charged particle optical system including a charged particle beam source configured to emit a charged particle beam, a plurality of lenses configured to focus the charged particle beam on a sample, and a deflector configured to scan the sample with the charged particle beam;

a detector configured to detect secondary charged particles, which are emitted due to an interaction between the charged particle beam and the sample, and output a detection signal; and

a calculation unit configured to calibrate first image data generated based on the detection signal output from the detector when the sample is two-dimensionally scanned with the charged particle beam, so as to generate second image data, wherein

the deflector two-dimensionally scans the sample with the charged particle beam by repeating scanning with the charged particle beam in a first direction while shifting a position in a second direction orthogonal to the first direction, and

the calculation unit generates the second image data using n first signal profiles each of which corresponds to a signal strength distribution in the first direction and which are extracted from the first image data, and a power spectral density P(f) (f: spatial frequency) of a window function corresponding to a signal processing delay in the detector.