  CP-PACS and JLQCD collaborations are carrying out a joint project of the 2+1
flavor full QCD simulation. Gauge configurations are generated for the
non-perturbatively $O(a)$-improved Wilson quark action and the Iwasaki gauge
action using PHMC algorithm at three lattice spacings, $a\sim 0.076$, 0.010 and
0.122 fm, with a fixed physical volume $(2.0 fm)^3$. We present analysis for
the light meson spectrum and quark masses in the continuum limit, which are
determined using data obtained from the simulations at the two coarser
lattices. Our simulations reproduce experimental values of meson masses. The ud
and strange quark masses turn out to be $m_{ud}^{\bar{MS}}(\mu=2 GeV)=3.34(23)
MeV$ and $m_s^{\bar{MS}}(\mu=2 GeV)=86.7(5.9) MeV$. We also show preliminary
results at our finest lattice spacing for which simulations are still being
continued.
