Provided is a detection method and device for analyzing trace substance of interest in a short time and with high accuracy without the need of performing any treatment for binding a fluorescent substance to the substance of interest or using any large apparatus. The substance of interest is detected by being immobilizing on a surface of any one of a hole transport layer, an electron transport layer, a luminescent layer, a buffer layer, and inside surfaces of electrodes for an organic electroluminescent device based on a change in at least one luminescent property selected from luminescence intensity, luminous efficiency, and emission spectrum of the organic electroluminescent device before and after the immobilization of the substance of interest.