An object is to provide a fuel supply system having a filler neck formed easily with high accuracy. A fuel supply system is configured to supply fuel ejected from a fuel nozzle to a fuel tank. The fuel supply system comprises a filler neck including a resin filler neck body and a metal retainer. The filler neck body is formed in a tubular shape and has an opening end arranged to form an opening which the fuel nozzle is inserted through. The retainer is placed to cover at least part of the opening end of the filler neck body and is joined with the filler neck body in at least part of the filler neck body by thermal welding.