Abstract: An oil changer comprises at least piping 5, 9, 10, along which an oil pump 12 and switching valves 8a, 8b are disposed, and first and second oil reservoirs 3, and 4. Used oil in an oil use location is recovered into the oil reservoir 4 via the piping, while unused oil in the first oil reservoir 3 is supplied into the oil use location via the piping. In this case, a flowmeter 11 for measuring an oil flow rate, as well as air sensors 6a, 6b for detecting the existence of air in used and/or unused oil when the air happens to exist in a flow of the used or unused oil and for outputting a predetermined signal, are provided at intermediate positions along the length of the piping 5, 9, and 10. Furthermore, a control section is provided into which the flow rate signal from the flowmeter 11 is inputted and which normally counts the number of the flow rate signals, but does not count them when the predetermined signal is inputted.