  We investigate the anisotropic lattice with $O(a)$ improved quark action as a
candidate of framework in which we can treat both the heavy and light quark
region in the same manner and systematically reduce the systematic
uncertainties. To examine applicability of anisotropic lattice, we calculate
the charmed meson spectrum and decay constants in quenched approximation. We
find consistent result with most advanced results on isotropic lattices.
