We compared the results of the optimum circular interpolation with those of the clothoid interpolation and the automatical circular interpolation function in the Maple NC automatic programming system, for three types of contour: an ellipse, an involute and a parallel index cam profile. The amount of interpolation data obtained by the optimum circular interpolation is less than that obtained by the Maple system. In particular, the reducing effect becomes obvious for a contour curve with a steep change in radius of curvature. Although the optimum circular interpolation is slightly more disadvantageous than the clothoid interpolation in terms of the amount of interpolation data, it is very practical and useful because the interpolation data can be directly applied in a general NC machine tool and the interpolation data for any offset curve can be direct obtained from those for the original curve.