A fuel tank opening and closing device is equipped with a tank opening forming member equipped with an injection port forming member having an insertion path and a tank side path arranged outside and inside an injection port, an injection port opening and closing mechanism for opening and closing the injection port, an insertion path forming member, and a drainage mechanism having a drainage path that connects the insertion path and the outside, and exhausts to the outside fuel that has accumulated inside the insertion path, and barrier members arranged on the drainage path. The barrier members are arranged with a labyrinth as the drainage path so that the insertion path cannot be seen from outside.