A direct and real-space study of the surface electronic structure on Cu-9at.%Al(111) alloy surfaces was performed using low-temperature scanning tunneling microscopy. The standing waves on Cu-9at.%Al(111)-(1×1) and (root3xroot3)R30surfaces, which were obtained by controlling annealing temperature, were observed by differential-conductance mapping. Surface imperfection caused by segregation of aluminum atoms acted as static scattering centers in order to sustain the standing-wave formation. An analysis of the standing waves revealed a significant downward energy shift of the Shockley surface states on both surfaces. This shift is explained in terms of the strong redistribution of the surface electrons.