This paper describes the experimental result on the relation between real contact area and wringing force of gauge block. The real contact area of wrung gauge blocks is measured by means of the application of the total reflection method which was already developed by Y. Sakurai, one of the authors. A polarized parallel light beam is projected on the hypotenuse plane of a rectangular glass prism beneath which a gauge block is wrung, and polarizers are adjusted so as to intercept the reflecting light from the metal surface. Thus, the contact parts are observed as dark images in light back ground. The total contact area is measured by a photoelectric method. The wringing force is measured by torque to make slide for wringing off the gauge block from the plate. It is clarified that the real contact area is approximately in proportion to the wringing force. Moreover, the measuring error of the contact area caused by an obscurity of the images accompanied by total reflection is discussed.