  The orbits of two black holes which are initially unbound can be transformed
into bound orbits by emitting gravitational waves during close encounters in a
star cluster, which is called a gravitational wave (GW) capture. The effects of
spin of black holes on GW capture are investigated in the context of numerical
relativity. The radiated energy during the encounter is dependent on the
effective spin when the black holes have the equal masses as expected from
post-Newtonian approximation. The strongest emission is produced when the spins
of both black holes are anti-aligned to the orbital angular momentum in the
case of fly-by encounters. But the opposite is true in the case of direct
merging: the strongest emission comes from the black holes with aligned spins
to the orbital angular momentum. The fraction of direct merging among the GW
captures increases in proportional to $v^{4/7}$ assuming the uniform
distribution of pericenter distances in the encounters, where $v$ is the
velocity dispersion of cluster, which means about 5 % of GW capture leads to
the direct merging for star clusters with $v=150$ km s$^{-1}$.
