Opening / closing device for a fuel tank

There is provided an opening / closing device for a fuel tank. The opening / closing device for the fuel tank includes a a fuel passage forming portion which is adapted to form a fuel passage, which is arranged to introduce a liquid fuel supplied to the fuel tank; an insertion-side opening / closing mechanism, which is adapted to open the fuel passage and to close; is a tank-side opening / closing mechanism, which is located on a fuel tank side of the insertion-side opening / closing mechanism and adapted to open the fuel passage and to close; a liquid delivery path which is adapted to permit connection of a portion of the fuel passage between the insertion-side opening / closing mechanism and the tank-side opening / closing mechanism with the vicinity of the opening / closing device; and to be open to the liquid delivery and to close and open toward the vicinity of the opening / closing device, an opening / closing valve is adjusted. This construction of the opening / closing device for the fuel tank reduces the penetration of dust and the like from the environment into the fuel passage through which a liquid fuel is performed.