  We present a lattice QCD calculation of phase shift including the chiral and
continuum extrapolations in two-flavor QCD. The calculation is carried out for
I=2 S-wave $\pi\pi$ scattering. The phase shift is evaluated for two momentum
systems, the center of mass and laboratory systems, by using the finite volume
method proposed by L\"uscher in the center of mass system and its extension to
general systems by Rummukainen and Gottlieb. The measurements are made at three
different bare couplings $\beta = 1.80$, 1.95 and 2.10 using a renormalization
group improved gauge and a tadpole improved clover fermion action, and
employing a set of configurations generated for hadron spectroscopy in our
previous work. The illustrative values we obtain for the phase shift in the
continuum limit are $\delta$(deg.) $= - 3.50(64)$, $ - 9.5(30)$ and $ -
16.9(64)$ for $\sqrt{s}({\rm GeV})$ $=0.4$, $ 0.6$ and $ 0.8$, which are
consistent with experiment.
