  We present a holographic dual of four-dimensional, large N_c QCD with
massless flavors. This model is constructed by placing N_f probe D8-branes into
a D4 background, where supersymmetry is completely broken. The chiral symmetry
breaking in QCD is manifested as a smooth interpolation of D8 - anti-D8 pairs
in the supergravity background. The meson spectrum is examined by analyzing a
five-dimensional Yang-Mills theory that originates from the non-Abelian DBI
action of the probe D8-brane. It is found that our model yields massless pions,
which are identified with Nambu-Goldstone bosons associated with the chiral
symmetry breaking. We obtain the low-energy effective action of the pion field
and show that it contains the usual kinetic term of the chiral Lagrangian and
the Skyrme term. A brane configuration that defines a dynamical baryon is
identified with the Skyrmion. We also derive the effective action including the
lightest vector meson. Our model is closely related to that in the hidden local
symmetry approach, and we obtain a
Kawarabayashi-Suzuki-Riazuddin-Fayyazuddin-type relation among the couplings.
Furthermore, we investigate the Chern-Simons term on the probe brane and show
that it leads to the Wess-Zumino-Witten term. The mass of the \eta' meson is
also considered, and we formulate a simple derivation of the \eta' mass term
satisfying the Witten-Veneziano formula from supergravity.
