PURPOSE: To extend the life of an organic electroluminescent element by preventing oxygen and moisture from entering a sealing material which is in liquid form.

CONSTITUTION: A transparent container 2 retaining an element and a container 4 retaining a sealing material 3 are disposed inside a vacuum deaerating vessel 1, and the transparent container 2 is immersed in the sealing material 3 in a high vacuum made by deaeration. Then an inert gas is introduced to inject the sealing material 3 into the transparent container 3, and the normal pressure is restored to seal the sealing hole 5 of the transparent container 2 with the sealing material.