Understanding the effects of each component of a molecular device is at the heart of designing a useful device. Molecular cores and linkers are well studied, but relatively few studies have been devoted to investigating the electrode effect on a molecular electronic device. Here, we study unique characteristics of Au, Ru, and carbon nanotube electrodes using the nonequilibrium Green function method combined with a density functional theory. By systematic modification of the device region, we extract the effect of the electrode materials on the electron transport. We show that the band structure and surface density of states of an electrode material, independent of the choice of other device components, have unique influences on the transmission curve. We note that carbon nanotube electrodes can offer unusual nonlinear current-voltage characteristics.