1. A method of measuring a shape of repeated patterns using a scanning electron microscope, comprising the steps of: capturing an image of a specimen at a scaling factor which permits a plurality of patterns under measurement to appear within a field of view; creating a plurality of profiles in a shape measuring area corresponding to each of the plurality of patterns under measurement; calculating an average profile by averaging the plurality of profiles created in all the shape measuring areas corresponding to the plurality of patterns under measurement; and determine shape roughness for the shape measuring area corresponding to each pattern under measurement using the average profile and the plurality of profiles created in the shape measuring area of each pattern under measurement.