This paper describes the principle of the noncontact fuel level sensor which consists of rods around which Ni wire is wound. The wires are heated by a constant current. This sensor makes use of the phenomenon of heat transfer by convection. Because there is a difference in the thermal resistance which occurs between sensor and air and between sensor and fuel, the sensor can detect fuel level. We can ensure that sensor output is not affected by inclination or acceleration. This sensor unit can be placed anywhere in the fuel tank. Since temperature change in the environment affects fuel level, the conventional level sensor which detects only fuel level is affected. But in our fuel level sensor, sensor output is automatically compensated for when the environment temperature changes.