PURPOSE: To measure the level of lubricating oil accurately and conveniently and to measure the performance and contaminated state of the lubricating oil, by applying a pulse voltage to a pair of electrodes, which are immersed in the lubricating oil when the temperature of the lubricating oil to be measured is at a specified temperature, and detecting a peak current value, a rate of current change, and the like.

CONSTITUTION: When the fact that the temperature of lubricating oil is at a specified temperature is detected by an oil-tank detecting means 2, a power source means 3 is actuated, and a pulse voltage is applied to a pair of electrodes 1 and 1, which are immersed in the lubricating oil. Then a transient current flows through the electrodes 1 and 1 and the current is detected by a current detecting means 4. The peak current value corresponding to the level of the lubricating oils is determined by a processing circuit means 5. The rate of current change corresponding to the characteristics of the lubricating oil based on internal resistance and capacity corresponding to dielectric constant is also determined by the processing circuit means 5. Then a display means 6 and a level display means 7 are controlled. In this constitution, the level of the lubricating oil is measured accurately and conveniently, and the performance and contaminated state of the lubricating oil are measured.