A fuel tank fuel filler structure comprising: a fuel fill inlet member that is equipped with a fuel fill inlet into which a fuel nozzle for fueling a fuel tank is inserted; an opening-and-closing valve that is capable of opening and closing the fuel fill inlet; a rotational member for attaching the opening-and-closing valve to the fuel fill inlet member in such a way that the opening-and-closing valve is rotatable between a closed position in which the opening-and-closing valve closes the fuel fill inlet and an open position in which the opening-and-closing valve opens the fuel fill inlet as a result of being pushed by the fuel nozzle; a guide member that guides the fuel nozzle to the opening-and-closing valve at a time of insertion of the fuel nozzle into the fuel fill inlet; and an interlock member that allows the guide member to move interlockingly with the rotation operation of the opening-and-closing valve in such a way as to enlarge an insertion region of the fuel nozzle when the opening-and-closing valve is in the open position, wherein, when fuel is to be fueled into the fuel tank, the opening-and-closing valve is first pushed by the fuel nozzle to open with the fuel nozzle, and wherein, when the fuel nozzle is pushed into the fuel fill inlet, then the guide member moves interlockingly with the rotation operation of the opening-and-closing valve fuel tank fuel filler structure being characterized in that the guide member is disposed on the opening-and-closing valve and has a rotational shaft that is disposed on the opening-and-closing valve in a site separated from a center of rotation of the opening-and-closing valve; and a guide plate whose one end is rotatably supported on the rotational shaft, and the interlock member has a biasing member that biases the guide plate toward the withdrawal region in a state where the opening-and-closing valve is in the open position. a fuel fill inlet member that is equipped with a fuel fill inlet into which a fuel nozzle for fueling a fuel tank is inserted; an opening-and-closing valve that is capable of opening and closing the fuel fill inlet; a rotational member for attaching the opening-and-closing valve to the fuel fill inlet member in such a way that the opening-and-closing valve is rotatable between a closed position in which the opening-and-closing valve closes the fuel fill inlet and an open position in which the opening-and-closing valve opens the fuel fill inlet as a result of being pushed by the fuel nozzle; a guide member that guides the fuel nozzle to the opening-and-closing valve at a time of insertion of the fuel nozzle into the fuel fill inlet; and an interlock member that allows the guide member to move interlockingly with the rotation operation of the opening-and-closing valve in such a way as to enlarge an insertion region of the fuel nozzle when the opening-and-closing valve is in the open position, wherein, when fuel is to be fueled into the fuel tank, the opening-and-closing valve is first pushed by the fuel nozzle to open with the fuel nozzle, and wherein, when the fuel nozzle is pushed into the fuel fill inlet, then the guide member moves interlockingly with the rotation operation of the opening-and-closing valve fuel tank fuel filler structure being characterized in that the guide member is disposed on the opening-and-closing valve and has a rotational shaft that is disposed on the opening-and-closing valve in a site separated from a center of rotation of the opening-and-closing valve; and a guide plate whose one end is rotatably supported on the rotational shaft, and a rotational shaft that is disposed on the opening-and-closing valve in a site separated from a center of rotation of the opening-and-closing valve; and a guide plate whose one end is rotatably supported on the rotational shaft, and the interlock member has a biasing member that biases the guide plate toward the withdrawal region in a state where the opening-and-closing valve is in the open position.