The light output surface structure layer has a concavo-convex structure on a surface opposite to the organic EL element. The concavo-convex structure includes flat surface portions parallel to one surface of the organic EL element and an inclined surface portion tilted relative to the flat surface portions. The projected area which is formed by projecting the inclined surface portion in a direction perpendicular to the flat surface portions onto a plane parallel to the flat surface portions is equal to or less than 0.1 times the total area of the flat surface portions. On a cross section of a flat surface portion cut along a plane parallel to the width and thickness directions thereof, the ratio H/W is 1 or greater and 2.5 or less, where H and W are the height and the width thereof, respectively.