of the objects are concentrated around $R_{\rm{c}} - K' \sim 3--4$, which is consistent with the color of early-type galaxies of cluster members at the corresponding redshifts and is also consistent with the results of shallower observations by Stanford et al.(1998) for MS $0451.6-0305$.

There are 2(8) EROs in the MS $0451.6-0305$ region with $R_{c}-K' \geq$ 6.0(5.3), and the number density is 0.5(2.0) arcmin$^{-2}$ down to $K'=$20.8 \[it is the limit of $R_{\rm{c}}-K'>5.3$ with $R_{\rm{c}}<26.1$ (R$_{\rm{ST}}<26.5$) sample\], simply dividing the surveyed area (4 arcmin$^{2}$) without any correction for lens amplification. When limiting the magnitude with $K'=$20.0, the numbers are reduced to 2(5). For MS $0440.5+0204$, there are 0(5) EROs with $R_{\rm{c}}-K' \geq$ 6.0(5.3), and the uncorrected number density is 0.0(1.25) arcmin$^{-2}$ down to $K'=$21.0. When limiting the magnitude with $K'=$20.0, the numbers are reduced to 0(3).

figure 2 shows 3-color ($R_{\rm{c}}$,$I_{\rm{c}}$,$K'$) image of MS $0451.6-0305$ with 2$\times$2field of view. There are some red objects which are bright in the $K'$ band. figure 3 shows the sky distributions of EROs in MS $0451.6-0305$ and MS $0440.5+0204$, respectively for showing clustering properties in each field. It is clear that both in the MS $0451.6-0305$ and the MS $0440.5+0204$ regions, there is a 