PURPOSE: To thoroughly deaerate the inside of a vessel and to produce a sintered body without oxidation by admitting gaseous Ar into the vessel in which metal or alloy powder is packed and welding a cover with a vent hole to the vessel, then sealing the vent hole.

CONSTITUTION: Commercially marketed pure iron powder 6 contg. oxygen is packed into the bottomed vessel formed by welding, for example, a vessel side part 1 and a vessel side part 2 by a weld zone 3. The cover 4 with the vent hole 5 is then put thereon. While the gaseous Ar is admitted from the vent hole 5 into the vessel, the cover 4 is welded to the weld zone 3' and thereafter, the vent hole 5 is connected to an evacuation system. While the inside of the vessel is deaerated, the vessel is heated to a prescribed temp. and the pressure therein is reduced to a prescribed vacuum degree, then the hole 5 is sealed. Such vessel is subjected to a hot hydrostatic press molding treatment, by which the sintered body contg. oxygen at a low ratio is obtd.