This research presents vision-based measurement of twodimensional positioning errors of machine tools. In experiment, we attach a charge coupled device (CCD) camera to a spindle to view an artifact of the known form accuracy. The edge in the vision is detected by using the Sobel operator and the position of the camera with respect to the artifact is measured from it. In this paper, we use a grid evaporated on a glass plate as an artifact to measure straightness and squareness of the drive system. For comparison, we measure them with an eddy-current displacement sensor and a square edge. By using this measurement result, we evaluate the accuracy of this visionbased measurement.