An apparatus for indicating the quantity of fuel in a vehicle. A variable resistance device, consisting of a bar resistor having its ends short-circuited and a slide, provided with a float, mounted on a guide bar, converts changes in fuel quantity into changes in electrical resistance which are indicated by a fuel gauge. The variable resistance device has a non-linear change in resistance with the maximum resistance when the slide is positioned at the middle part of the resistor. The pointer of the fuel gauge moves in one direction and then reverses direction in response to the non-linear resistance change, with the one-half tank level being the turning point. A lamp in the fuel gauge is actuated by a detection switch when the one-half tank level is reached so that the lamp indicates to the vehicle operator that the gauge is measuring the remaining one-half of the fuel.