  We report on the PACS-CS project focusing on a direct simulation of 2+1
flavor QCD on the physical point and chiral analysis of meson and baryon masses
off the physical point with both the SU(2) and SU(3) chiral perturbation
theories. Configurations are generated with the O(a)-improved Wilson quark
action and the Iwasaki gauge action. The up-down quark is simulated by
employing the DDHMC algorithm with several improvements and the UV-filtered
PHMC algorithm is implemented for the strange quark. We investigate the
convergence behaviors of the SU(2) and SU(3) chiral expansions up to NLO for
the pseudoscalar meson sector, where the up-down quark mass ranges from 3 MeV
to 24 MeV and the strange quark mass is chosen around the physical value. The
fit results for the low energy constants are compared with those recently
obtained by other groups. We also discuss the importance of the direct
simulation at the physical point by comparing the physical quantities measured
on the physical point with those estimated by the extrapolation method.

High Energy Physics - Lattice