  We derive the linear Langevin equation that describes the behavior of
critical fluctuation above the critical temperature of the chiral phase
transition in the Nambu-Jona-Lasinio model. The Langevin equation relaxes
exhibiting oscillation and shows thermalization. The relaxation becomes slower
as the system approaches the critical point(the critical slowing down). The
time correlation function also calculated using the Langevin equation shows
that there exists the same soft mode as the previous calculation in the linear
response theory.
