1. A three-dimensional measurement method for measuring three-dimensional coordinates of a feature point of a measurement target using at least two cameras in accordance with a stereo measurement method, comprising the steps of: capturing the feature point using a first camera, and capturing a feature point group continuous with the feature point using a second camera based on data of a predetermined shape of the measurement target, wherein the feature point is not within a field of view of the second camera; calculating a plane including a corresponding point on a sensor plane of the first camera, the corresponding point corresponding to the feature point, a focal position of the first camera, and a focal position of the second camera, and calculating a first line that is a line of intersection of the calculated plane and a plane including a sensor plane of the second camera; calculating a second line including a corresponding point group on the sensor plane of the second camera, the corresponding point group corresponding to the feature point group; calculating a corresponding point on the plane including the sensor plane of the second camera, the corresponding point on the plane including the sensor plane of the second camera corresponding to the feature point, by determining an intersection of the first line and the second line; and calculating a straight line extending through the corresponding point on the sensor plane of the first camera and the focal position of the first camera, and a straight line extending through the corresponding point group on the sensor plane of the second camera and the focal position of the second camera, and calculating an intersection of the calculated straight lines as three-dimensional coordinates of the feature point.