PURPOSE: To execute a drying operation at a high degree of cleanliness by a method wherein a porous member is impregnated with a liquid, it is heated and the liquid is discharged from fine holes on the surface.

CONSTITUTION: A vapor generation apparatus 5 is provided with a porous sintered alloy member 6 in which fine spaces have been formed. A hollow body 7 in which many small holes 8 for organic-solvent impregnation use have been made uniformly is buried at the inside of the member 6. An organic solvent 11 inside a tank 10 is supplied to the hollow body 7 through a liquid supply route 9, and impregnates the member 6 from a group of the small holes 8. The member 6 is heated by a heat block 14; the solvent 11 is gasified; a vapor 15 is generated uniformly from the whole surface of the member 6 into a vapor tank 2. Thereby, a foreign body is not contained in the vapor 15, and a drying operation at a high degree of cleanliness can be executed.