To provide a measuring method which enables the speedy and easy measurement of the concentration of benzene by concentrating the concentration of benzene in the atmosphere and provide a filter system for concentration used for the method.

A mixture gas of benzene and air is passed from a supply side of a higher molecular demarcation membrane, which is capable of dissolving benzene more than air, to its permeation side. By selectively dissolving benzene in the demarcation membrane and simultaneously diffusing benzene dissolved in the demarcation membrane to the permeation side of the demarcation membrane, the concentration of benzene in the mixture gas is made fifty times higher on the permeation side than on the supply side of the demarcation membrane in a benzene concentration process. The method for measuring the concentration of benzene in air includes the benzene concentration process. In the filter system for concentration, the high molecular demarcation membrane is extended in a filter housing.