An organic electroluminescent (EL) device which contains a novel coumarin derivative composed of a coumarin ring, a naphthalene ring with one or more hydrocarbon groups, and a five-membered hetero ring condensed with the naphthalene ring so as to give an electronic resonance through the coumarin and naphthalene rings. The coumarin derivative emits a visible luminescence with a satisfactory color purity, which consistently continues over a long period of time even at an elevated temperature when used in such an organic device.