An aircraft water tank constituting an aircraft water tank is provided with a cylindrical section, dome sections, and mouthpieces. The mouthpieces are provided with mouthpiece bodies and annular wall sections that extend outward in the radial direction around the entire outer circumferences of the mouthpiece bodies between an inner liner and a fiber-reinforced resin layer, and are attached to the inner liner and the fiber-reinforced resin layer around the circumferences of openings. Outer surfaces of the annular wall sections contacting the fiber-reinforced resin layer are formed by uniform tension curved surfaces.