A method and system for imaging an object to be inspected and obtaining an optical image; creating a reference image from design pattern data; preparing an inspection recipe including one or more templates and parameter settings necessary for the inspection; checking the pattern and the template against each other, and selecting the reference image which corresponds to the template; detecting first and second edges in the selected reference image in accordance with the parameter setting using determined coordinates as a reference; detecting first and second edges in the optical image, this optical image corresponds to the selected reference image; and determining an inspection value by acquiring the difference between the line width of the optical image and the reference image using the first edge and second edge of the reference image and the first edge and second edges of the optical image.