PURPOSE: To prevent a gas sensor from being deteriorated by supplying air into a gas sensor chamber when the sort of fuel oil is identified and oil filling is started.

CONSTITUTION: An oil filling apparatus main 1 is provided with an air pump 6 and an oil filling nozzle 2 is equipped with an ejector 40 which works on compressed air and produces negative pressure, a gas sensor chamber 24 communicating with a vapor vent port 49 and a switching valve 25 which is interlinked with the motion of a nozzle lever to change air supply over to either the ejector 40 or the gas sensor chamber 24. A switching device 25 has a diaphragm 31 to receive the liquid pressure inside the oil filling nozzle 2, and the switching valve 25 is activated by the displacement of the diaphragm 31, so that air is supplied into the sensor chamber 24 to scavenge vapor.