  We investigate quark deconfinement by calculating the effective potential of
the Polyakov loop using the non-perturbative propagators in the Landau gauge
measured in the finite-temperature lattice simulation. With the leading term in
the 2-particle-irreducible formalism the resultant effective potential exhibits
a first-order phase transitions for the pure SU(3) Yang-Mills theory at the
critical temperature consistent with the empirical value. We also estimate the
thermodynamic quantities to confirm qualitative agreement with the lattice data
near the critical temperature. We then apply our effective potential to the
chiral model study and calculate the order parameters and the thermodynamic
quantities. Unlike the case in the pure Yang-Mills theory the thermodynamic
quantities are sensitive to the temperature dependence of the non-perturbative
propagators, while the behavior of the order parameters is less sensitive,
which implies the importance of the precise determination of the
temperature-dependent propagators.
