A saddle-riding type vehicle having a vehicle fuel tank assembly comprising: a fuel tank mounted on the saddle-riding type vehicle in an inclined attitude in a front-to-rear direction of the vehicle and having a flat shape elongated in the front-to-rear direction; and a fuel pump unit installed in the fuel tank by inserting the fuel pump unit into the fuel tank through a bottom wall of the fuel tank; wherein the fuel pump unit includes a main body, a support body extending from an upper part of the main body in a longitudinal direction of the elongated fuel tank, and a fuel level gauge supported and extending on the support body; wherein the fuel level gauge includes a fuel level gauge body, a float arm pivotally supported at its proximal end by the fuel level gauge body for up and down swinging movement, and a float supported on a free end of the float arm; wherein the float arm, in a highest swing position thereof, extends in the longitudinal direction of the fuel tank and is set to take the highest swing position in an intermediate height level of the fuel tank; wherein the support body is formed with a cutout (38b3) in a lower edge thereof, and the cutout (38b3) has a first width in the direction in which the support body extends, and a second width in a vertical direction perpendicular to the direction in which the support body extends, the first width being greater than the second width, wherein the direction in which the support body extends from the main body of the fuel pump unit is the same as the direction in which the float arm extends in the highest swing position; and wherein the fuel tank is mounted on the saddle-riding type vehicle in a forwardly declining attitude, the fuel pump unit is arranged in a front part of the fuel tank, and the support body and the float arm in the highest swing position extend rearward. a fuel tank mounted on the saddle-riding type vehicle in an inclined attitude in a front-to-rear direction of the vehicle and having a flat shape elongated in the front-to-rear direction; and a fuel pump unit installed in the fuel tank by inserting the fuel pump unit into the fuel tank through a bottom wall of the fuel tank; wherein the fuel pump unit includes a main body, a support body extending from an upper part of the main body in a longitudinal direction of the elongated fuel tank, and a fuel level gauge supported and extending on the support body; wherein the fuel level gauge includes a fuel level gauge body, a float arm pivotally supported at its proximal end by the fuel level gauge body for up and down swinging movement, and a float supported on a free end of the float arm; wherein the float arm, in a highest swing position thereof, extends in the longitudinal direction of the fuel tank and is set to take the highest swing position in an intermediate height level of the fuel tank; wherein the support body is formed with a cutout (38b3) in a lower edge thereof, and the cutout (38b3) has a first width in the direction in which the support body extends, and a second width in a vertical direction perpendicular to the direction in which the support body extends, the first width being greater than the second width, wherein the direction in which the support body extends from the main body of the fuel pump unit is the same as the direction in which the float arm extends in the highest swing position; and wherein the fuel tank is mounted on the saddle-riding type vehicle in a forwardly declining attitude, the fuel pump unit is arranged in a front part of the fuel tank, and the support body and the float arm in the highest swing position extend rearward.