PURPOSE: To make it possible to detect abrasion dust of iron at work site simply and quantitatively as occasion calls, by a method wherein a device having a smooth, thin and impermeable film of a nonmagnetic substance is provided on the upper surface of a flat-plate-shaped magnet so that a tilt angle from a horizontal plane is variable.

CONSTITUTION: A glass plate 2 as a thin impermeable film of a nonmagnetic substance is brought into close contact with the upper surface of a flat-plate-shaped magnet 1 and they are set on a base 3, while a tilting support block 4 supports the lower part of the base 3 at one point so that the base 3 is supported at a variable tilt angle α around the end part of the base whereat it is grounded on a horizontal plane LV. A device thus constructed is tilted at a prescribed angle α and a prescribed amount of lubricating oil sample 5 is dropped gently onto the surface of the plate 2 at the upper part tilted. Then the sample 5 flows down on the surface of the plate 2 and dust of a magnetic material of iron contained therein is attracted to be left on the surface of the plate 2 in the course of the flow by the magnetism of the magnet 1 in the lower part. Based on the amount of the residual oil attracted, the shape of the dust, etc., accordingly, the properties of the sample can be detected simply and easily in a comparative and empirical manner and necessary judgement and process can be made even at a work site.