  We investigate the liquid-gas phase transition of dense matter in supernova
explosion by the relativistic mean field approach and fragment based
statistical model. The boiling temperature is found to be high (T_{boil} >= 0.7
MeV for rho_B >= 10^{-7} fm^{-3}), and adiabatic paths are shown to go across
the boundary of coexisting region even with high entropy. This suggests that
materials experienced phase transition can be ejected to outside. We calculated
fragment mass and isotope distribution around the boiling point. We found that
heavy elements at the iron, the first, second, and third peaks of r-process are
abundantly formed at rho_B = 10^{-7}, 10^{-5}, 10^{-3} and 10^{-2} fm^{-3},
respectively.
