Abstract: A method of deciding the quality of a measurement value of the line width, the line interval or the like of a pattern on an object to-be-measured, including acquiring the signal intensity distribution of the pattern on the object to-be-measured, detecting the edge positions of the pattern from the acquired signal intensity distribution, detecting the taper widths of the edge parts of the pattern from the acquired signal intensity distribution, and deciding that the measurement value calculated on the basis of the detected edge positions is correct, when the detected taper widths fall within a predetermined range set beforehand. In this way, it is permitted to automatically decide the defective measurement of the line width of the pattern, or the like, attributed to an unclear image due to inferior focusing in an image photographing mode, an unclear image due to an image drift ascribable to charging-up, or the like.

Abstract: A method of deciding a measurement value as decides the quality of the measurement value of the line width, the line interval or the like of a pattern on an object to-be-measured, comprising the steps of acquiring the signal intensity distribution of the pattern on the object to-be-measured (2 in FIG. 1), detecting the edge positions of the pattern from the acquired signal intensity distribution, detecting the taper widths of the edge parts of the pattern from the acquired signal intensity distribution, and deciding that the measurement value calculated on the basis of the detected edge positions is correct, when the detected taper widths fall within a predetermined range set beforehand. In this way, it is permitted to automatically decide the defective measurement of the line width of the pattern, or the like, attributed to an unclear image due to inferior focusing in an image photographing mode, an unclear image due to an image drift ascribable to charging-up, or the like.