To provide a lubricating device capable of accurately informing the residual amount of a liquid fuel by a simple structure.

This lubricating device 1 comprises a pressure sensor 6 in a lubricating pipe 5 connecting a fuel tank 2 to a device 3. A control means 7 detects a residual oil amount Q in the fuel tank 2 based on detected pressure by a pressure sensor 6. The control means 7 recognizes the detected pressure P when the fuel tank 2 is full of the liquid fuel as full pressure Pmax, and based on the full pressure, detects the residual oil amount Q. The control means 7 recognizes that an air inclusion state is eliminated on the assumption that the detected pressure P detected by the pressure sensor 6 exceeds the full pressure Pmax set beforehand, and updates the full pressure Pmax.