Recent large-scale galaxy spectroscopic surveys, such as the Sloan Digital Sky Survey (SDSS), enable us to execute a systematic, relatively unbiased search for galaxy clusters. Such surveys make it possible to measure the 3D distribution of galaxies but are hampered by the incompleteness problem due to fiber collisions. In this study we aim to develop a density-measuring technique that alleviates the problem and derives densities more accurately by adding additional cluster member galaxies that follow optical color-magnitude relations for the given redshift. The new density measured with both spectroscopic and photometric data shows a good agreement with apparent information on cluster images and is supported by follow-up observations. By adopting this new method, a total of 924 robust galaxy clusters are found from the SDSS DR5 database in the redshift range 0.05<z=4)