  We report initial results for spectroscopic observations of candidates of
Lyman Break Galaxies (LBGs) at $z\sim5$ in a region centered on the Hubble Deep
Field-North by using the Faint Object Camera and Spectrograph attached to the
Subaru Telescope. Eight objects with $I_C\leq25.0$ mag, including one AGN, are
confirmed to be at $4.5<z<5.2$. The rest-frame UV spectra of seven LBGs
commonly show no or weak Lyalpha emission line (rest-frame equivalent width of
0-10\AA) and relatively strong low-ionization interstellar metal absorption
lines of SiII $\lambda$1260, OI+SiII $\lambda$1303, and CII $\lambda$1334 (mean
rest-frame equivalent widths of them are $-1.2 \sim -5.1 $\AA). These
properties are significantly different from those of the mean rest-frame UV
spectrum of LBGs at $z\sim3$, but are quite similar to those of subgroups of
LBGs at $z\sim3$ with no or weak Lyalpha emission. The weakness of Lyalpha
emission and strong low-ionization interstellar metal absorption lines may
indicate that these LBGs at $z\sim5$ are chemically evolved to some degree and
have a dusty environment. Since the fraction of such LBGs at $z\sim5$ in our
sample is larger than that at $z\sim3$, we may witness some sign of evolution
of LBGs from $z\sim5$ to $z\sim3$, though the present sample size is very
small. It is also possible, however, that the brighter LBGs tend to show no or
weak Lyalpha emission, because our spectroscopic sample is bright (brighter
than $L^{\ast}$) among LBGs at $z\sim5$. More observations are required to
establish spectroscopic nature of LBGs at $z\sim5$.
