et al. 2002; Frayer et al. 2003). EROs have red colors, which is consistent with elliptical galaxies at high redshift, and they are separated into two categories of dusty starburst population and passively evolved stellar systems. The former are believed to be young high-redshift objects with a large star-formation rate, and their features are consistent with forming elliptical galaxies based on theoretical predictions. Therefore, searching for EROs associated with faint SCUBA sources is one of the most effective methods for detecting obscured (dusty) star-forming galaxy at high redshift, though it may be limited only for z$\leq$3, because of large extinction of their optical(rest UV) light by their internal dust. There have been several studies (Smail et al. 1999; Ivison et al. 2000; Frayer et al. 2000; Barger et al. 2000; Lutz et al. 2001; Frayer et al. 2003) which identified the ERO counterparts of the sub-mm sources. Furthermore, Ivison et al.(2000) succeeded to obtain the redshifts of SCUBA sources at $z \sim 2.56$ and $z \sim 2.2$ in the A 1835 region, and there are some lower redshift samples with spectroscopically determined redshifts(e.g. Smith et al. 2001). The lack of a suitable sample is partly because of their optical faintness. 