PURPOSE: To provide a pressure vessel without any stress concentration parts by placing the plates having edge parts opposite to each other to the center part to make the edge parts abutted on each other, setting the width of the edge parts so as to obtain the volume of the molten metal to form the desired bead, and executing the welding of the edge parts without using a filler metal.

CONSTITUTION: Plates 1,2 are placed opposite to each other, and the edge parts 1a, 2a are abutted on each other, and these abutted edge parts 1a, 2a are welded without using a filler metal. The base material of the edge part is melted by the welding heat input, and the molten metal of the amount corresponding to the width B is provided. The shape of the welded part becomes a bead shape of the butt-welded joint, and the stress concentration is not easily generated even by the higher inner pressure. The welding method where no filler metal is used, such as TIG welding and the laser beam welding is used. This constitution melts the base material of the edge parts 1a,2a of the plates 1,2 and provides the molten metal instead of the filler metal, enabling the welding without using the filler metal. No stress concentration part is made for the inner pressure, and this method can be used in manufacturing a pressure vessel.