Abstract: In accordance with the present invention, the method of manufacturing a vacuum chamber which is used as a cluster tool, a vacuum film-forming apparatus, or the like of a manufacturing apparatus used for semiconductors, liquid crystals, solar cells, and the like, and which is formed by a vessel in which an opening (4A) is provided at one surface for forming a cover, and a hole (4) smaller than the opening (4A) is provided in an opposite surface to the opening (4A), includes the steps of:by using a forging press which is provided with an outer die (3) and an inner die (2) for die forging a material (1-1),cutting the material to dimensions suitable for the die forging of the material (1-1) which is made of a metal;heating the material (1-1) to a temperature for die forging;placing the heated material (1-1) in the outer die (3) of the press, and pressing the inner die (2) against the material (1-1) by the forging press to effect forging; andsubjecting the forged material to machining into a predetermined configur