A fueling device comprises a passage-forming member, an opening-forming member configured to form an opening, a filler port open-close mechanism that includes an open-close member configured to open and close the opening, a screwing mechanism that includes an outer circumferential threaded section and an inner circumferential threaded section and a gasket placed between the opening-forming member and the passage-forming member to seal between the opening-forming member and the passage-forming member, wherein the outer circumferential threaded section is provided on outer periphery of the passage-forming member, the inner circumferential threaded section is provided on the opening-forming member and screwed to the outer circumferential threaded section, the opening-forming member is attached to the passage-forming member by screwing the outer circumferential threaded section to the inner circumferential threaded section.