  We analyzed the statistics of subhalo abundance of galaxy-sized and
giant-galaxy-sized halos formed in a high-resolution cosmological simulation of
a 46.5Mpc cube with the uniform mass resolution of $10^6 M_{\odot}$. We
analyzed all halos with mass more than $1.5 \times 10^{12}M_{\odot}$ formed in
this simulation box. The total number of halos was 125. We found that the
subhalo abundance, measured by the number of subhalos with maximum rotation
velocity larger than 10% of that of the parent halo, shows large halo-to-halo
variations. The results of recent ultra-high-resolution runs fall within the
variation of our samples. We found that the concentration parameter and the
radius at the moment of the maximum expansion shows fairly tight correlation
with the subhalo abundance. This correlation suggests that the variation of the
subhalo abundance is at least partly due to the difference in the formation
history. Halos formed earlier have smaller number of subhalos at present.
