The purpose of the present invention is to increase work efficiency and reduce component costs and weight, while maintaining the strength of a cylindrical part in the section surrounding a tank port. A tank port (18) includes a reinforcement sheet (28), an inner member (30) and an outer member (32). The reinforcement sheet (28) is attached to the outer peripheral surface of a cylindrical part (12) in the section surrounding a through hole (1202). An inner attachment plate part (3004) of the inner member (30) is attached to the inner peripheral surface of the cylindrical part (12), and an inner cylindrical part (3002) is inserted into the through hole (1202). An outer cylindrical part (3202) of the outer member (32) is attached to the outer peripheral surface of the inner cylindrical part (3002) protruding from an opening (2802), and an outer attachment plate part (3204) is attached to the reinforcement sheet (28) in the section surrounding the opening (2802). The section of the cylindrical part (12) surrounding the entire periphery of the through hole (1202) is sandwiched and reinforced by the inner attachment plate part (3004) and the reinforcement sheet (28).