A method of evaluating image pattern output accuracy based on numerical and objective criteria, by employing quality engineering. The method includes setting command signals which provide different distances from a reference point to at least three other points; outputting an image pattern which indicates reference coordinates of the reference point and distant measurement coordinates of the at least three points; optically reading the image pattern; obtaining data of the reference coordinates and the distant measurement coordinates from the read image pattern; calculating each distance between the obtained reference coordinates and the obtained distance measurement coordinates and outputting output signals which respectively provide the calculated distances; and calculating based on the command signals and the output signals, an S/N ratio for indicating a degree of dispersion of the output signals with respect to the command signals and a sensitivity of the output signals with respect to the command signals.