  Chiral symmetry at finite temperature is studied using the Schwinger-Dyson
equation.
  We calculate numerically the critical temperature using the Schwinger-Dyson
equation with the gauge parameter that depends on an external momentum.
  The critical temperature obtained by this method is similar to that with the
Landau gauge and wave function renormalization constant 1. Moreover, the gauge
invariance in the ladder approximation is examined using our method.
