  We investigate the structure of the dark matter halo formed in the cold dark
matter scenario using $N$-body simulations. We simulated 12 halos with the mass
of $6.6\times 10^{11}M_{\odot}$ to $8.0\times 10^{14}M_{\odot}$. In almost all
runs, the halos have density cusps proportional to $r^{-1.5}$ developed at the
center, which is consistent with the results of recent high-resolution
calculations. The density structure evolves in a self-similar way, and is
universal in the sense that it is independent of the halo mass and initial
random realization of density fluctuation. The density profile is in good
agreement with the profile proposed by Moore et al. (1999), which has central
slope proportional to $r^{-1.5}$ and outer slope proportional to $r^{-3}$. The
halo grows through repeated accretion of diffuse smaller halos. We argue that
the cusp is understood as a convergence slope for the accretion of tidally
disrupted matter.
