1. A method of correcting a contour of a grayscale image based on an image processing process carried out by a computer, said method comprising: generating a distance contour image representing a contour extracted from a distance image whose pixels include distance values and a grayscale contour image representing a contour extracted from a grayscale image whose pixels include gradation values, from a subject; determining whether there is a contour in a region on said distance contour image whose coordinate position corresponds to that of a region which includes a portion of the contour of said grayscale contour image; and correcting the contour of said grayscale image if it is judged that there is said contour in said region, wherein said correcting the contour of said grayscale image corrects the contour of said grayscale image by placing a calculated distance image differential value into a function formula, and applying a result of the function formula to the grayscale image, and wherein said function formula is expressed as: 
 contour of processed grayscale image=contour of grayscale image to be processed+constant×(constant×distance image differential value×grayscale image differential value) 1/2 .