  Numerical simulation of lattice QCD is now an indispensable tool for
investigating non-perturbative properties of quarks at low energies. In this
paper, I introduce a recent lattice QCD calculation of light hadron spectrum
and quark masses performed on a dedicated parallel computer, CP-PACS. From a
simulation of QCD with two flavors of dynamical quarks, we find
$m_{ud}^{\bar{\rm MS}}(2{\rm GeV}) = 3.44^{+0.14}_{-0.22}$ MeV for the averaged
mass of $u$ and $d$ quarks to reproduce the experimental masses of $\pi$ and
$\rho$ mesons, and $m_{s}^{\bar{\rm MS}}(2{\rm GeV}) = 88^{+4}_{-6}$ MeV or
$90^{+5}_{-11}$ MeV to reproduce the $K$ or $\phi$ meson mass. These values are
about 20--30% smaller than the previous estimates using the quenched
approximation.
