  High-accuracy rotation curves of spiral galaxies show a steep rise in the
central few hundred pc region, indicating high concentration of mass toward the
center. Using the rotation curves, we idrectly calculate radial distributions
of the surface-mass density (SMD), and obtain radial profiles of the
mass-to-luminosity ratio (M/L). The M/L ratio is found to vary significantly
not only in the massive halo but also within the bulge and disk regions. It
increases with the radius within the disk, and rapidly toward halo. In some
galaxies, the M/L increases inward toward the center within the bulge,
indicating a massive dark core. On these bases, we discuss the radial
distribution of dark matter in spiral galaxies.
