  In this paper, we investigate the structure of condensation fronts from warm
diffuse gas to cold neutral medium (CNM) under the plane parallel geometry. The
solutions have two parameters, the pressure of the CNM and the mass flux across
the transition front, and their ranges are much wider than previously thought.
First, we consider the pressure range where the three phases, the CNM, the
unstable phase, and the warm neutral medium, can coexist in the pressure
equilibrium. In a wide range of the mass flux, we find solutions connecting the
CNM and the unstable phase. Moreover, we find solutions in larger pressure
range where there is only one thermal equilibrium state or the CNM. These
solutions can be realized in shock-compressed regions that are promising sites
of molecular cloud formation. We also find remarkable properties in our
solutions. Heat conduction becomes less important with increasing mass flux,
and the thickness of the transition layer is characterized by the cooling
length instead of the Field length.
