Abstract: An external force is periodically applied to an object to be measured, a two-dimensional surface of the object is resolved and scanned by suitable infrared radiation detection means, and the infrared radiation at the times of maximum and minimum loading by the external force are detected for the respective resolved zones. The difference between the infrared radiation at the maximum and the minimum loading times is then calculated for every resolved zone. Further, the calculated values are multiplied by correction values corresponding to the shape, material, infrared radiation rate and so forth of the object. The thus obtained values are suitably visibly indicated in the positions of the respective zones. This indication is ordered by suitably slicing the levels of the thus obtained values to identify and display them in accordance with an ordering scheme.