Provided is a method for determining the magnification of a pattern searching template of a scanning electron microscope. The determining method comprises: acquiring a first image initially at a first magnification; then acquiring a second image which contains a pattern image displayed on the first image at a second magnification lower than the first magnification; making the size of the first image coincident with the size of a third image which cut out a portion of the second image; thereafter determining the correlation value between the first image and the third image; and setting the second magnification as the magnification of a pattern searching template, in the case where the correlation value is equal to or higher than a predetermined value. As a result, a condition for acquiring a search area can be properly set, when pattern recognition is performed by means of the template.