PURPOSE: To correct illuminance unevenness by minimizing loss of quantity of light, by providing an absorbing film and a transmission increasing film on the surface of a lens so as to reduce the quantity of transmitted light in the central part of the lens and increase the quantity of transmitted light in the peripheral part thereof.

CONSTITUTION: The surface 7 of a lens 6 is coated with an absorbing film 9 of which thickness is the largest at its central part and decreases gradually towards the peripheral part 8 thereof. Close to this absorbing film 9 is provided a transmission increasing film 10 of which thickness increases towards the peripheral part 8. In this setting, when an original plane 5 is illuminated flatly, the relation between incident angle θ and illuminance will be as shown by dotted line (b). If the lens 6 is coated only with the absorbing film 9, the relation will be as shown by by solid line (a). Therefore, when the lens 6 is coated with absorbing film 9 and transmission increasing film 10, the illuminance is even, and the loss of quantity of light is small.