Fuel tank manufacturing method and fuel tank

A method of manufacturing a fuel tank, comprising:

• passing a hollow molten resin projection, that projects-out in a wall-thickness direction and is formed at a molten resin sheet that becomes a tank structural member structuring a tank main body, through a mounting hole of a part-to-be-mounted that is placed on the molten resin sheet;
• and
• pressurizing the molten resin projection from an inner side, and causing at least a portion of the molten resin projection to jut-out to a peripheral portion of the mounting hole of the part-to-be-mounted, wherein
• a projecting member, that projects-out from a mold surface at which the molten resin sheet is placed and that forms the molten resin projection at the molten resin sheet, is provided at a molding die for molding the tank structural member,
• an elastic body, that expands due to supply of a non-compressible fluid and pressurizes the molten resin projection from an inner side, is provided at the projecting member,
• the molten resin projection is formed by the projecting member at the molten resin sheet that is placed along the mold surface, and
• the elastic body is expanded due to supply of the fluid, and pressurizes the molten resin projection from the inner side.