Respective glass substrates 1 of a pair of such EL devices 3 are disposed in such a manner that EL element portions 2 formed on their respective front surfaces 1a are opposed to each other. Spacers 4 are disposed between the two glass substrates 1 so that the EL element portions 2 are separated from each other and do not interfere with each other. In this state, peripheral portions of the two glass substrates 1 are bonded to each other with a sealing material 5, whereby a hollow portion 6 formed between the two glass substrates 1 is sealed with the sealing material 5 and isolated from the outside. Then, the two glass substrates 1 that are integrated together are immersed in an etching liquid, that is, they are subjected to thinning processing.