1. A three-dimensional-position measuring method, comprising the steps of: a) inputting images of an object viewed from a plurality of points of view through image inputting means; b) detecting change of orientation of said image inputting means, occurring when said step a) is performed; c) detecting change of position of point of view, occurring when said step a) is performed; d) extracting characteristic points from the image which is input in said step a) previously, each of said characteristic points corresponding to a respective one of objects points on said object; e) extracting corresponding points from the image which is input in said step a) currently, each of said corresponding points corresponding to a respective one of said characteristic points; and d) calculating the three-dimensional position of each of said object points, based on the change of orientation and the change of position of point of view of said image inputting means and said characteristic points and said corresponding points.