An urging structure for a lid includes a spring member having one spring end linked to a supply-port-forming member and the other spring end linked to a lid, and provided so as to be most elastically deformed at an intermediate position between a closed position and a maximum open position of the lid to urge the lid. The spring member is linked to the lid in such a way so as to vary a distance between the other spring end and a turning center of the lid, and the distance stays constant when the lid is in the closed position and in the intermediate position, increases in a process of moving from the intermediate position to the maximum open position, and becomes maximum when the lid is in the maximum open position.