PURPOSE: To obtain a compact high in shape accuracy by charging powder in a molding flask rigid to hydrostatic pressure, inserting a molding punch into the molding flask so that it can slide freely on the inside of the flask and driving it at a hydrostatic pressure to compact the powder.

CONSTITUTION: The molding flask 1 is a rigid molding flask made of material such as acrylic resin, etc., mounted on a press mold and the molding punch 2, too, is a rigid punch made of material similar to that of the flask. The structure of the molding flask can be made freely according to the shape of the compact but a builtup molding flask is preferred to improve the releasing property of the compact after it is molded. The rigid molding flask and the molding punch are light-weight and of low cost and can be made easily large-sized. In this way, the compact high in shape accuracy can be obtained easily and at low cost by carrying out cold hydrostatic press molding. Further, since this is a builtup molding flask, it can prevent generation of cracking surely in time of mold removal.