Pressure vessel

A pressure vessel comprising:

• a pressure vessel body provided with a flow channel through which a fluid is capable of flowing, having a rectangular cross-sectional shape, and formed to extend in a longitudinal direction;
• a body flange provided at at least one end side of the pressure vessel body in the longitudinal direction and having a circular cross-sectional shape;
• and
• a connecting member connecting the pressure vessel body and the body flange to each other,
• wherein the connecting member has
• a body-flange connected portion connected to the body flange and having a circular cross-sectional shape,
• a pressure-vessel-body connected portion connected to the pressure vessel body, being larger in cross section than the body-flange connected portion, and having a circular cross section, and
• a connecting portion connecting the body-flange connected portion and the pressure-vessel-body connected portion to each other and formed in a conical, hemispherical, or semi-elliptical shape with a size changing to be gradually smaller from the pressure-vessel-body connected portion toward the body-flange connected portion, wherein
• the pressure-vessel-body connected portion is formed such that one end side of the pressure vessel body is insertable and fittable in the pressure-vessel-body connected portion.