A data input system including electronic paper and a stylus writing device is disclosed. The electronic paper includes a transparent display substrate on which a number of optically readable code patterns have been formed, the optically readable code patterns representing positional information on a display surface, a rear surface substrate opposing the display substrate, and coloring particles that are enclosed between the display substrate and the rear surface substrate and that are movable by applying an electric or a magnetic field. The electronic paper displays an image due to motion of the particle. The stylus writing device includes a writing head provided at the end of the stylus for writing the image by applying an electric or a magnetic field to the electronic paper by contact and includes an optical reading device for optically reading the code patterns formed on the display surface where the end of the stylus contacts.