  We construct a self-consistent model which describes a black hole from
formation to evaporation including the back reaction from the Hawking
radiation. In the case where a null shell collapses, at the beginning the
evaporation occurs, but it stops eventually, and a horizon and singularity
appear. On the other hand, in the generic collapse process of a continuously
distributed null matter, the black hole evaporates completely without forming a
macroscopically large horizon nor singularity. We also find a stationary
solution in the heat bath, which can be regarded as a normal thermodynamic
object.
