  We report the discovery of a strong over-density of galaxies in the field of
a radio galaxy at z=1.52 (4C65.22) based on our broad-band and narrow-band
(H-alpha) photometry with Subaru Telescope. We find that H-alpha emitters are
located in the outskirts of the density peak (cluster core) dominated by
passive red-sequence galaxies. This resembles the situation in lower-redshift
clusters, suggesting that the newly discovered structure is a well-evolved rich
galaxy cluster at z=1.5. Our data suggest that the color-density and stellar
mass-density relations are already in place at z~1.5, mostly driven by the
passive red massive galaxies residing within Rc<200 kpc from the cluster core.
These environmental trends almost disappear when we consider only star-forming
(SF) galaxies. We do not find SFR-density or SSFR-density relations amongst SF
galaxies, and the location of the SF main sequence does not significantly
change with environment. Nevertheless, we find a tentative hint that
star-bursting galaxies (up-scattered objects from the main sequence) are
preferentially located in a small group at ~1-Mpc away from the main body of
the cluster. We also argue that the scatter of the SF main sequence could be
dependent on the distance to the nearest neighboring galaxy.
