A method for producing a substrate having an irregular concave and convex surface for scattering light includes: manufacturing a substrate having the irregular concave and convex surface; irradiating the concave and convex surface of the manufactured substrate with inspection light from a direction oblique to a normal direction and detecting returning light of the inspection light returned from the concave and convex surface by a light-receiving element provided in the normal direction of the concave and convex surface; and judging unevenness of luminance of the concave and convex surface by an image processing device based on light intensity of the returning light received. An organic EL element which includes a diffraction-grating substrate having an irregular concave and convex surface is produced with a high throughput.