PURPOSE: To measure the concentration of oil mist which is floating and suspended in air, by introducing air in a low boiling point organic solvent, arresting the oil mist, heating the oil mist, evaporating the organic solvent, and measuring the weight of the remaining oil mist.

CONSTITUTION: An impinger 1, a flowmeter 2, and a vacuum pump 3 are connected. A low boiling point organic solvent such as n-hexane is put in the impinger 1. The vacuum pump 3 is rotated and the pressure in the inside of the impinger 1 is reduced, and air is introduced. Oil mist in the introduced air is arrested by the n-hexane. A container, wherein the n-hexane is put, is mounted on a hot plate and heated to 80 degrees, and only the n-hexane is evaporated. Thereafter, the weight of the remaining oil mist is measured, and the concentration of the oil mist in the air is obtained.