Mounted within the measuring section (10) formed by two clamping devices (2, 4) are measuring rollers (8, 9) which deflect the test material (10). The deflection results in a force couple (P, P′) and a resultant force (R). The resultant force (R) is transferred into a load cell (3) via a link (6). This arrangement enables the clamping devices (2, 4) and the load cell (3) to be mounted separately. The measuring rollers (8, 9) are equipped with incremental transducers (19, 20) by means of which the clamp slippage (&Dgr;1) creeping out of the clamping faces of the clamping devices (2, 4) and the extension of the test material sections (10′, 10″) are measured.