PURPOSE: To eliminate an adverse effect of an electron beam on the heating and vaporization of molten metal by inclining at least the upper surface of a porous body impregnated with molten raw metal downward from the electron beam irradiation surface.

CONSTITUTION: The raw metal 13 from which an isotope is to be separated is placed in a vaporization crucible 12. The porous body 21 to be impregnated with the molten raw metal 13 is placed in the crucible 12, and an electron beam generator 14 for emitting an electron beam B to heat and vaporize the molten metal infiltrated in the porous body 21 is provided. Furthermore, at least the upper surface of the body 21 is inclined downward from the electron beam irradiation surface. Consequently, the molten porous component material does not remain on the electron beam irradiation part, and the heating and vaporization of the molten metal by the electron beam are not adversely affected.