PURPOSE: To heat a material to be treated in a short time and to improve the capacity in vacuum-evaproation recovery.

CONSTITUTION: A material 9 to be treated is fed into a vacuum furnace 8, and the material 9 is heated by a glow discharge with the material 9 as a cathode and the furnace 8 as an anode. As a result, the material 9 is heated at a high rate, and the vacuum evaporation of impurities is rapidly performed. The evaporated impurities are aggregated by an impurity treating device 13, solidified and continuously recovered. Consequently, the capacity in vacuum evaporation is enhanced.