  The formation of the Moon from the circumterrestrial disk has been
investigated by using $N$-body simulations with the number $N$ of particles
limited from $10^4$ to $10^5$. We develop an $N$-body simulation code on
multiple Pezy-SC processors and deploy FDPS (Framework for Developing Particle
Simulators) to deal with large number of particles. We execute several high-
and extra-high-resolution $N$-body simulations of lunar accretion from a
circumterrestrial disk of debris generated by a giant impact on Earth. The
number of particles is up to $10^7$, in which 1 particle corresponds to a 10
km-size satellitesimal. We find that the spiral structures inside the Roche
limit radius differ between low-resolution simulations ($N \leq10^5$) and
high-resolution simulations ($N \geq10^6$). According to this difference,
angular momentum fluxes, which determine the accretion timescale of the Moon
also depend on the numerical resolution.
