  We study the linearized kinetic equation of relaxation model which was
proposed by Bhatnagar, Gross and Krook (also called BGK model) and solve the
dispersion relation. Using the solution of the dispersion relation, we analyze
the relaxation of the macroscopic mode and kinetic mode. Since BGK model is not
based on the expansion in the mean free path in contrast to the Chapman-Enskog
expansion, the solution can describe accurate relaxation of initial disturbance
with any wavelength. This non-relativistic analysis gives suggestions for our
next work of relativistic analysis of relaxation.
