  We study the finite quark mass effects of the low-energy QCD using the
improved ladder Schwinger-Dyson and Bethe-Salpeter equations which are derived
in the manner consistent with the vector and axial-vector Ward-Takahashi
identities. The non-perturbative mass-independent renormalization allows us to
calculate the quark condensate for a non-zero quark mass. We explicitly show
that the PCAC relation holds. The key ingredients are the
Cornwall-Jackiw-Tomboulis effective action, the generalized Noether current and
the introduction of the regularization function to the Lagrangian. The
reasonable values of the pion mass, the pion decay constant and the quark
condensate are obtained with a rather large $\Lambda_{QCD}$. The pion mass
square and the pion decay constant are almost proportional to the current quark
mass up to the strange quark mass region. It suggests that the chiral
perturbation is applicable up to the strange quark mass region.
  We study the validity of the approximation often used in solving the
Bethe-Salpeter equations too.
