Correction of widths obtained by measurement of a sample with the use of a scanning electron microscope is executed with greater precision. A standard sample for correction comprises a plurality of correction mark members, the respective correction mark members, being lined up at specified intervals in a specified direction, and respective widths thereof, in the specified direction, differing from each other so as to be of respective sizes as pre-set. Measurement of the respective widths of the correction mark members is made to obtain respective measurement widths while authorized widths of the correction mark members are kept stored in an image processing unit of the scanning electron microscope to thereby find differences between the respective measurement widths, and authorized widths corresponding thereto, and the differences are stored as respective correction functions to correct the measurement width of the sample.