1. A method of determining the quality of Heart & Cupid optical effects of a diamond, including the steps of: reading out dimensions, which have been obtained by measuring a round brilliant cut diamond with an ID appended using a dimension measuring device, by computer graphics (referred to as “CG”) and outputting Heart & Cupid images and the ID or outputting Heart & Cupid images of the diamond taken by a CCD camera and an ID; storing data, such as the symmetry of eight heart marks, variation in the area of a heart, the displacement of the tip portion of each heart, the depth of a slit of each heart, a ratio of right and left shoulder widths relative to the overall width of each heart, a ratio of a distance in a boundary portion between each heart and a V-shaped mark located on the inner side on the radial line of the heart relative to the overall width of the corresponding heart, a ratio between the area of the V-shaped mark and the area of a standard heart, and a ratio between the right-side length of the V-shaped mark and the left-side length of the V-shaped mark, into a computer database; determining the ranking of the quality of the heart marks by performing arithmetic processing of the data; and storing data, such as the symmetry of eight cupid marks, a variation degree obtained from the ratio between the maximum value and the minimum value of each cupid area, whether a straight line connecting the outer tip portion, the intermediate intersection, and the center-side tip of each cupid overlaps another one or has a displacement with an angle, and whether the arrow tip portion of each cupid sharply abuts against a girdle or abuts against the girdle portion with a width, into a computer database and determining the ranking of the quality of the cupid marks by performing arithmetic processing of the data.