In order to clarify the propagation mechanism of dark spots in an organic multilayered electroluminescent device, in situ electroluminescence microscopy as well as photoluminescence (PL) microscopy and Auger electron spectroscopy of the degraded device was carried out. The difference in local PL spectra between the dark spots and the normal surface area was also observed by using scanning near-field optical/atomic force microscopy. The growing mechanism of the dark spots was proposed from these observations.