In a retaining piece interposed between the adjacent rolling balls, a concave surface of each of both side surfaces of the retaining piece where it contacts with the spherical surfaces of the balls is configured to partly contact with the spherical surface of the ball. It can refer to data stored in memory and complements configured according to the use, situation or environment of the location and purpose of the readerwriter, such as advertising or information relevant to the environment andor location, among other cases. The current path of the second transistor current path has substantially the same width and length as the first transistor current path. Thereafter, the input voltage is gradually dropped from the maximum voltage so as to be converged by using the constant current source.