At high redshift, formation of galaxies is biased to
the region of overdensity at larger scale.
SSA22 protocluster and the 'super structure' at z=3.09  is
one of the most prominent and well characterized
high density region at z>3 (Steidel et al. 2000; Yamada et al. 2012).
We have been conducting comprehensive studies of LyA emitters,
LyA blobs, red obscured galaxies, massive and passive galaxies,
and sub-mm and X-ray selected objects in this very interesting system.
In this talk, I will mainly discuss about "extremely dense
compact group" found at  the core of the protocluster
that consists of more than several redshift-confirmed
objects. Interestingly, two of the massive galaxies have
spectra of quiescent (no on-going star formation) galaxies
while rest of them are dusty red and diffuse star-forming
objects including the ALMA detected ones.
One of the quiescent object is an X-ray source.
We discuss the properties of the group as a progenitor of
the brightest cluster galaxy in the cluster today.
The work is published in Mariko Kubo et al. (2016).