  We present the results of near-infrared spectroscopic observations of the
$K$-band selected candidate galaxies in the protocluster at $z=3.09$ in the
SSA22 field. We observed 67 candidates with $K_{\rm AB}<24$ and confirmed
redshifts of the 39 galaxies at $2.0< z_{\rm spec}< 3.4$. Of the 67 candidates,
24 are certainly protocluster members with $3.04\leq z_{\rm spec}\leq 3.12$,
which are massive red galaxies those have been unidentified in previous optical
observations of the SSA22 protocluster. Many distant red galaxies (DRGs;
$J-K_{\rm AB}>1.4$), hyper extremely red objects (HEROs; $J-K_{\rm AB}>2.1$),
{\it Spitzer} MIPS 24 $\mu$m sources, active galactic nuclei (AGNs) as well as
the counterparts of Ly$\alpha$ blobs and the AzTEC/ASTE 1.1-mm sources in the
SSA22 field are also found to be the protocluster members. The mass of the
SSA22 protocluster is estimated to be $\sim2-5\times10^{14}~M_{\odot}$ and this
system is plausibly a progenitor of the most massive clusters of galaxies in
the current Universe. The reddest ($J-K_{\rm AB}\geq 2.4$) protocluster
galaxies are massive galaxies with $M_{\rm star}\sim10^{11}~M_{\odot}$ showing
quiescent star formation activities and plausibly dominated by old stellar
populations. Most of these massive quiescent galaxies host moderately luminous
AGNs detected by X-ray. There are no significant differences in the
[O{\footnotesize III}] $\lambda$5007/H$\beta$ emission line ratios, and
[O{\footnotesize III}] $\lambda$5007 line widths and spatial extents of the
protocluster galaxies from those of massive galaxies at $z\sim2-3$ in the
general field.
