to 300 mm desirable results are obtained as shown in fig2 the shape of the convex portions 17 on the reflective film 4 is so set that the angle u03b8 between the incident light and the reflected light 8 15 or 9 increases in going from the region a to the region b for this purpose the angle of reflection at the reflective subregions 13 is varied such that the angle u03b8 is obtained between the incident light and the reflected light for light rays 7 incident normal to the surface of the upper substrate 2 as shown in fig3 fig4 is a plan view of a reflective plate according to a first embodiment the reflective subregions 13 on the reflective plate 1 are regularly spaced from each other on the center line vertical bisector line 16 also the subregions are arranged on coaxial circles a 1 a n where n is an integer greater than unity centered at the center point 14 a placed on the center line the reflective subregions having the same angle between the incident light and the reflected light are positioned on the same coaxial line a multiplicity of reflective subregions having different angles of u03b8 1 u03b8 2 and u03b8 3 from the left side are placed the reflective subregions 13 on the coaxial circles reflect light incident from a direction vertical to the plane of the paper of fig4 and form the exit region 14 all the reflective subregions 13 are so arranged that the reflected light rays are concentrated at the center 12 of the exit region 14 since the device is so constructed in the first embodiment in.