In a first step, two conductive plates such as two zinc galvanized (electroplated) steel plates with films formed on surfaces thereof, are prepared; a flexible conductive material is held between these two zinc galvanized (electroplated) steel plates. A spacer is also held between the two zinc galvanized (electroplated) steel plates to regulate the space therebetween and a measurement object such as a conductive cloth is held between the flexible conductive material and at least one of the zinc galvanized (electroplated) steel plates. In a second step, the electric resistance between the two zinc galvanized (electroplated) steel plates is measured while the flexible conductive material is held together with the measurement object between the two conductive plates.