Light hadron spectrum and light quark masses from lattice QCD

We present recent results on the light hadron spectrum and light quark masses in lattice QCD, both in the quenched approximation and with two flavors of dynamical quarks. Simulations are made with a renormalization-group improved gauge action and a tadpole-improved clover quark action. Our new results in the quenched simulation are in good agreement with our previous calculation using the standard lattice action. A comparison between the results in full and quenched QCD clearly shows the existence of sea quark effects in meson and quark masses.