1. A position and orientation calculating method comprising the steps of: inputting a two-dimensional picture image of an object article obtained from an image detector; extracting at least two two-dimensional images from at least two windows defining image processing ranges corresponding to two portions of the object article in accordance with coordinates of each of said two windows, and extracting data describing coordinates of a sequence of points from a sequence of segments approximated as a polygon for an image designating a contour of a portion of the object article between each of said two windows; calculating a center of gravity from said data with respect to a pattern adapted for extraction of an entirety of a partial shape from said two two-dimensional images and calculating a straight line by a linear equation from said data with respect to the pattern adapted for extraction of the partial shape from said windows; and calculating calculated data describing position and orientation of the object article from said center of gravity and calculating the orientation of said object article from a combination of said center of gravity and the intersection of said straight line and a perpendicular line extending thereto from said center of gravity.