Abstract: A check is performed whether a terminating point distanced from said starting point in a distance corresponding to a one-eighth fraction of an entire circumferential length of the circle to be drawn is passed by the latest set point. When said terminating point is passed, drawing process is terminated. If the terminating point is not passed, all points symmetric to the set point with respect to at least one straight line selected from a group of the straight line Y=X, the X-axis and the Y-axis are derived for use in drawing the circle. Next, the X coordinate of the set point is varied. Then, a value for judgment associating with variation of the X coordinate of the set point with the latest value for judgment is calculated. Thereafter, a check is performed whether a distance between the Y coordinate of a first varied point where only the X coordinate is varied from the set point and the true Y coordinate on the circle at the same X coordinate is less than 0.5 or not.