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)~((MS)-bar) (2 GeV) = 3.44_(-0.22)~(+0.14) MeV for the averaged mass of u and d quarks to reproduce the experimental masses of π and ρ mesons, and m_s~((MS)-bar) (2GeV) = 88_(-6)~(+4) MeV or 90_(-11)~(+5) MeV to reproduce the K or φ meson mass. These values are about 20-30% smaller than the previous estimates using the quenched approximation.
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